The old Puyo Puyo style and characters were better, but Fever is the most balanced Puyo to date. You can now prevent huge attacks from dropping in 2-player by constantly chaining, and then even cancel the attack totally by triggering Fever. It makes for very good 2-player matches.
In the old Puyo games, a huge attack would mean almost certain death as you only had one move to try and cancel it. So Puyo Puyo Fever just edges out Puyo Puyo Sun in my books as the best one in the series. It did very well in Japan, so who knows we might get a follow-up to Fever where they bring all the old characters back.
I'm personally not a fan of 4-player Puyo, as the game is more like a fighting-game and that works best 1-on-1. The 4-player modes in Puyo's like the DC version were too random, so your attacks were spread out against the other people you were playing rather than you choosing someone to attack. So that meant weak players are always knocked out first. It's a mess. Actually, everything about the DC version was a mess - special attacks, NO!