Having stayed at the Mercure Sevilla hotel in Havana - I would not agree that this was 4 star.
We booked through Solitair Holidays - I know now a bad move - be warned of this company.
Mercure Sevilla gave us so called 4 star rooms with views of walls - literally no light coming into the rooms - very oppressive.
They were expecting us to leave a day earlier than we had paid for - this could be down to Solitair Holidays however the whole thing took time and effort to sort out.
There are far nicer hotels in Havana to stay at.

Stayed here for 2 nights at the start of a three week trip to Cuba. Arrived immediately after 10 hour flight from London. Immediately impression was of an old colonial hotel somewhat faded over the years - potentially a rather interesting introduction to Cuba we thought.

However things started to go rapidly downhill once we got to out room. On the plus side the rooms are very large and well appointed, in a rather old fashioned kind of a way - no problem with that given the nature of the hotel. The real negative points were as follows:
a) the room was damp and literally stank of mould. The wardrobe area was most obviously affected. Luckily we were only here two nights and were able to live out of our suitcases.
b) the staff all gave the impression that they didn't really want to be there. We devised a game of trying to get at least one of them to smile. We failed!

Perhaps the staff were all rejects from the Parque Central Hotel just around the corner. We stayed there for three nights at the end of our holiday. The comparison could not have been more stark.

During our three week stay in Cuba we stayed in five hotels in different parts of the island. The Sevilla was by far the worst. Thank goodness it was only two nights at the start of our holiday. If you start here as we did don't worry; things can only get better.

A lovely old building, staff typically Cuban (very friendly, but rather unenthusiastic).
Rooms a little tired, but full of character.
The hotel's location is perfect-on the edge of the old town, and not too far from the sea-front.
Leave any preconceptions or expectations of super-luxury behind, and you'll have a great time.

Hotel Sevilla is a beautiful turn of the century hotel with a Moorish ornate facade and ceramic tiles decorating the spacious lobby. It is now under the French chain Accor and quite a few of the staff speak French. You will be walking in the footsteps of Fidel Castro and Al Capone, and Graham Greene's "Our Man in Havana" was set here. Should you wake up in the middle of the night with a craving for a mojito (4CUC), the El Patio Sevillano bar is open 24 hours a day. You can get a pizza there for 7 CUC and listen to second-rate Cuban music groups in the evenings. As well, on the last day we were leaving very early, and we were able to get a free continental breakfast (coffee + toast) there.
Breakfast buffet (7 to 10 am) was in a large, attractive room and provided good food. The selections included cheeses, cold cuts, fruits, cereals, rice, saussages, and omelettes/pancakes/eggs made to order. Yes, as some people complained in their reviews, sometimes they ran out of cups and coffee and we had to wait a bit, but in my opinion, this is no reason to lose your cool. You are on holidays, after all, and this is Cuba. If you want more luxury and a reportedly amazing buffet, pay more to stay in the nearby Parque Central, but the lobby of that hotel is like central station and Sevilla has an intimate feel in spite of its size.
We stayed on the 7th floor in the corner room, which had two large windows, a beautiful view of El Morro, comfortable bed, white-tiled bathroom, and great furniture. It appears, however, that the standard of rooms is quite varied within the hotel. On the last day, we talked to a couple who had a very bad experience with their rooms (changed a couple of times), which were reportedly moldy, with only a twin bed, and other shortcomings. We were shocked, as our experience was totally different, even though we also booked our holiday with Sunwing.
If you want a shot of grandeur, have dinner in the Roof Garden restaurant on the top floor. You will pay quite a bit and enjoy a great view (especially if your room window faces a wall). We did not eat there, but this restaurant is considered the best in town. The swimming pool is quite large and beautiful - you can see it from the street. The New Year's buffet was served in that area, and synchronized swimming ballet was part of the entertainment. Very nice for 55 CUC per person, unless you were part of a package vacation, in which case it was free.
More about the money: the hotel has a 24-hour exchange desk, but the rate is a bit better at the CADECA -- there is branch two minutes away - just outside the gate by the elevators. Visa is accepted (but not issued by American banks), and we used it to pay for of our daytrips (through our Sunwing rep). By the way, it appears that if you book through the travel agency (beside the above-mentioned CADECA), you will most likely get a larger bus with the washroom. I found this out through a bit of a mix-up and that's what I would do next time. It seems that fewer people book through the Sunwing rep - the bus is smaller and the guides do not speak English as well. At least, that was our experience.
In the lobby of the hotel, there are two computers and, for a fee (I am not sure if it was 6CUC per hour or half an hour) you can access the internet. The connections are very slow, so you may need an hour and a lot of patience...
The location of Hotel Sevilla was excellent, if your aim is to get to know old Havana. You can walk everywhere and feel safe. There are cabs outside the door of the hotel and you get approached every time you leave, but all you have to do is smile and say "not today". You do have to get used to many offers and saying "no". Next to the hotel, there are the two major sights: the Museo de la Revolucion (worth a visit to see the interior of the presidencial palace) and the Museo Nacional de Bellas Artes with its Cuban art collection, which is a must for anybody even slightly interested in art.
If you would like to get a snack nearby, the restaurant Y Prado Y Neptuno is within a 5-minute walking distance and has good pizza for 6.50 CUC. It is on Prado, at... yes, Neptuno :-) basically beside Hotel Inglaterra. We went there a few times. By the way, accross the street from the Hotel Inglaterra, you can take a hop-on-hop-off bus for 5 CUCs which will take you around Havana, including Vedado and Miramar neighbourhoods. We got off at the cemetary, which was an interesting place. Another bus from the same stop will take you to the beach for 3 CUCs. We didn't do this, but saw the crowd at around noon - maybe it's less crowded earlier in the morning.
Some people reviewing this hotel focussed on the negatives. Well, it is true that the plumbing is old and that the toilet plugged up easily. The water temperature varied throughout the shower, especially during peak times. The lock did stick on the inside and the once white towels were grey. BUT, if you have a decent room, these were minor inconveniences and the reason I am mentioning them is to remind those complainers that this is a communist country where people make $8 a month (an equivalent of two mojitos) and don't have enough food. The beautiful houses in old Havana are in a complete state of disrepair. There is a shortage of... everything. So, be glad that you are coming from the land of plenty and if waiting for a cup is spoiling your holiday, you need to go somewhere else.
Final notes: 1) bring all your photographic needs with you, including extra batteries, as there is a photo around EVERY corner. You can recharge in the room - the electricity and outlets are the same as in Canada/US. 2) remember to leave a CUC a day on the pillow for the cleaning staff. And, 3) if you want to see the most radiant smiles on children's faces, bring packages of pencil crayons and give them to the children on the street (for example just on the other side of Prado (Paseo de Mart). Next time, we will take some balls for the boys as well. Havana is an amazing, unforgettable city that will steal your heart -- don't let minor inconveniences annoy you enough to dampen this experience.