Stayed at the Helikon for two nights as part of a cycling tour. The hotel was chosen by the tour company. Overall, the expeience was enjoyable. My room was a decent size, comfortable, and clean. The bathroom was also nice & clean. The location directly on Lake Balaton and the lake views from the room are just fantastic. And it's only about a 15 minute walk into the heart of Keszthely. The downside, as noted by other reviewers, is the nightly invasion of bugs that take place. Although they look like mosquitoes, they actually aren't mossies and don't bite. But that doesn't make their presence in your room or the dining room any more welcome. This could be alleviated if the hotel had central air conditioning.

Stayed 7 nights at this hotel on half board basis in September 2008. There were 4 of us in our party, 2 of which had single rooms. All the rooms were the same size with twin beds, however, our room was in the renovated part of the hotel. It was much better than the 2 single travellers rooms, freshly painted and newly carpeted. All the rooms had the same layout and faced some part of the lake. The bathrooms were nicely appointed with bath, rather on the small size, with an overhead shower, WC, basin and hair dryer - very clean, all be it a little cramped. Balcony was rather small. There was a problem with ventilation as the only opening was the large balcony door. It was very hot the first few days of our stay and it was difficult to leave the door open because of the insects, it would have been nice to have some aircon.
Rooms were cleaned daily. My bed was in desparate need of replacement, springs were almost coming through ! however, the others in the party were quite satisfied with theirs.
The food in our opinion was very good, both breakfast and the evening meal were buffet style, and there certainly was a great variety of food, nicely cooked and presented. Plates were cleared away very efficiently by the dining room staff who were all very friendly as were all the staff we had dealings with.

Negatives -
My dreadful mattress
No Tea/Coffee facilities in the room
There appeared to be only one means of escape if there was a fire, and that was in the centre of the hotel- not very good!

The hotel is located right by the lake with its own mini-island which is accessible via a bridge directly from the hotel. The staff is rather friendly, and my room was quite spacious with the usual appliances one expects from a hotel (in case you have difficulty finding the fridge; it is concealed under the tv). The lake is reasonably nice, if not shallow. There is also a swimming pool that is open till 9pm. The breakfast is quite decent, and includes fruits, cereals, scrambled eggs, tea, coffee, milk, and other things one normally finds at a hotel breakfast. The hotel is in decent shape, and rooms are cleaned every day. That would be the end of my review if not for the ventilation problem.

The problem is that there are hordes of mosquitoes that become active at night. There are also somewhat active during the during the day, but at night they reign over the lake and the shore. The problem is that the rooms have no air-conditioning, and mosquitoes prevent opening the window (unless you prefer becoming mosquitoes' breakfast rather to the death by suffocation). For a reason which defies any rational explanation, the window does not have a mosquito net. Given reasonably high temperatures during the summer. I did not open the window during the night, and opened it only very reluctantly during the day, because I still had to get rid of the few mosquitoes that would get in. I should mention that the fan in the bathroom does not work (it was not only my room, but several other guests also mentioned that) despite there being a button that is supposed to activate it. That makes it even harder to cope with the closed window.

Finally, though it did not affect me since I stayed alone. I heard one of the guests complain that they received only one key for a double room.

Planned to stay longer, but checked out after one night! At a quarter to seven in the morning someone (using a key) entered our room! My husband called out, so whoever it was quicky left. When we told the front desk, they said housekeeping do not start until 7 am. They suggested it was probably another guest?!
Also, as we were packing to leave (before check out time), a very stern woman entered (again with a key, no knock whatsoever) - she basically barged in, yelled at us in Hungarian (I told her politely, still in shock at her intrusion, we don't understand Hungarian) so she yelled at us in English, hands on hips, if we had taken anything from the mini bar. I said No, and she then opened it to check it herself. Satisfied I was not lying, and indeed had not taken anything, she marched back out. My husband and I couldn't believe it! In all the years we have travelled,we have never experienced this!
When we informed the front desk about this woman, a lady at the desk did apologize for this intrusion!
Beware!! Very overpriced for what you get! (We paid 110 Euros plus taxes) Airconditioning does not function well, and even though we had non-smoking room (and maybe floor?) very smoky.

Don't go there! There are other nice looking hotels - we wished we had gone to the Bacchus.
We then decided to go to neighbouring town of Heviz which is lovely!