I went there in 2005, so may be things have changes, but I wouldn't go there twice.
The best thing about the place is its central location (close to bars, clubs and a small sandy beach) on the beach front line.
My single room was rather spacious with some basic furniture, but the AC didn't bring relief. They didn't change obviously old towels until I requested.
The service was neutral, even indifferent. The reception guy was sometimes glued to the monitor, being slow issuing the key. Once there was a situation where I even received a rather humiliating comment from a reception lady.
My biggest complain though is poor food. I had BB, and the choice was narrowed to a few pieces of bread, cheese and ham, really not much. On the other hand, the restaurant is capable of good stuff. Once I had dinner at their cafe, which is just opposite the hotel with a great seaview, and it was really good. The waiter was super friendly.
Someone might say that's right for the money you pay, but next year I paid the same amount of money for two weeks at a better place instead of one week.
Despite that I'd had my best holiday ever, and didn't pay much attention to the hotel at that time, but started analyzing only back home. The place is rather Ok for someone on tight budget, but with a condition you go out during all day and return to the place just for some hours of sleep. That's precisely what I did.

We stayed just for 2 nights in the Flisvos Beach Hotel in the middle of June. Although there was nothing technically wrong with the hotel, we weren't particularly impressed. The room was clean and a decent size, though the bath was tiny and the water pressure in the shower was poor. We regularly travel in Greece and are used to the basic accomodation, but felt that Hotel Flisvos was overpriced considering how basic it was. Breakfast was included but no hot food; the website states that "Beach service is offered on the beach with sunchairs and umbrellas" but doesn't mention that you have to pay for the use of these sunchairs and umbrellas; the room had no additional facilities that you wouldn't get in a hotel half the price.

Overall, the hotel is fine but nothing special and certainly not worth the price.