Check in was ok, room was pretty basic but bed was full of bed bugs, bathroom was pretty run down, but breakfast was good

I booked Mercure on the Accor website for a special rate (55 euro) that required full prepayment online. I paid with my credit card. But upon my arrival to the hotel the receptionist refused to check me in, she said that I may had paid by a stolen credit card, and so I had to leave a cash deposit of at least 100 euros.
It had to argue for half an hour, then the GM interfered and I finally got my room key. A second disappointment came when I realized that the A/C was not working. It was + 34 C. This was the receptionist's comment: I am not a technician, I dont know why the a/c doesnt work. You may open the window and turn off the light to avoid mosquitos.
The A/c is centrally controlled, when the hotel is not fully booked the managers can turn a/c off to save electricity which is quiet expensive in France. After two day and many complains the a/c was turned on again and i was upgraded to a premium room with a fantastic view of the Notre Dam de la Garde.

The room was big enough with king bed, plasma tv, safety deposit box, luxury bathroom (most french hotels only have shower), separate wc, coffee maker.

Mercure is a tall modern tower conveniently located two blocks from the Marseille old port.

When looking for the hotel go to the Centre Bourse shopping centre (actually Mercure has a direct access to it which was closed during my stay), or look for the open air museum of history of Marseille, Mercure is the tall brown tower behind it. No taxi driver in Marseille would know a small side street - Neuve St Martin.

Also i understand that the garbage bins outside the hotel are beyond the control of Accor group but it could be a good idea to encourage the municipality to remouve them.
Besides that the location is very convinient, next door to shops, museum and a stone's throw from the port. Convenient if you want to explore Marseille on foot.

In hot weather you may prefer to take a tourist train from the port area to go to the Notre Dam de la Garde hill or old blocks on the opposite. Usually I am not a fan of kitschy touristy entertainments but in such heat (and some sanitary pbms of this port city) trains were very convenient.
Another "thing not to miss" is a boat trip to Chateau d'If - setting to the famous Count of Montecristo novel.
So I think you cant beat the Mercure location and price (if the hotel agrees to check you in).
Some nice SPA hotels are also located in the estern bay to the left of the port, but they would be expensive and you would need to take taxi to get downtown.

Mercure offer breakfast for 13 euros per person, but no dinner of lunch (may be it will open in high season?). There is a nice bar in the lobby.

My general impressions of Marseille are also mixed: its so big, so picturesque, so old, so romantic, and ..as all the ports so dirty. Still it is a pleasure just to be there, look at the beautifull sailboats, watch this mixture of people so different in appearance and culture: sailors, tourists, immigrants.

The hotel is very well located, 5min walk from the old town and the port. The staff is very friendly and helpful. Breakfast is very good with a lots of choices. The parking is just under the hotel which usually cost 15 euros per day but we only paid 8 euros for the whole weekend.
The room is clean with an amazing view of Notre dame de la garde (8th floor).

This is without a doubt the worst hotel I have ever been in. There is no way it is a three star hotel. The staff was rude and disinterested. It took us almost 30 minutes to check in because the people at the desk kept stopping to answer the phone or talk to each other. The elevators were so small we were unable to fit in with our luggage and one other person. They were also very slow. The room was tiny and very dirty. The carpet had not been cleaned maybe since the hotel was built. The bed was little more than an old mattress on the floor. The towels in the bathroom were worn thin and the bath towels were the size of hand towels. The maid refused to give us more than two. The rooms were not soundproof and you could hear traffic from the street and people in other rooms. The hotel lobby and bar were shabby and the staff barely acknowledge we were there. We could not get out of there fast enough! You can get a much better hotel for the same price in Marseille. Keep looking!