I LOVE this show and is one of my top favorite sitcoms along with 30 rock, the office, parks and rec and married with children. I'm surprised to see so many people dislike Nick because him and his cynicism is my favorite character. The guys and their dynamic/chemistry is actually the best part of the show, better than the other actually romantic relationships. When they built a blanket fort and sang "I wanna know what love is", the best.
To be honest I do agree with other reviewers that Jess is super annoying. I think I realize this somewhere around Season 2. By the time her and Nick get together shes super controlling of the relationship and I pretty much stop liking her at that point. As seasons progress I guess her real personality of being judgmental and a know it all is super apparent by Season 4. I loved Season 1 Jess who was more awkward and light hearted, couldn't stand her by the end and enjoyed the polar opposite character of Megan Fox's Regan joining.
I also liked a lot of the secondary characters I wish got more time. I actually love Principal Foster and the school staff scenes. The principal was another cynical opposite to Jess' eternal optimism and it was great comedy. I also loved the ditzy nurse though I could be biased because I loved her in Parks and Rec. Outside Dave is a major fave but again biased, I mean cmon its Steve Agee. Although I can understand the concerns of prejudice, with Nadia's character Cece's roommate.
Another props goes out to the soundtrack, often at the bar playing in the background. Where have all the cowboys gone by Paula Cole, not sure I've ever heard that ever on another show. Black velvet by Alannah Myles. The show should have done more of nostalgic jams integrated, they did a great job in Season 1 but then it became less of an occurrence.
All in all, love this show and enjoy revisiting.