School Rumble is a high school romantic comedy. To be frank, I don't think it has many merits. Jay, you probably shouldn't read this one; I may be about to rip it a new one and I know it's one of your favorites.
It's not a total failure. It does have some funny moments, though most are at the risk of complete absurdity. In fact, as the show goes on, it gets increasingly more absurd. I know it's difficult to discuss anime in the realm of reality, but School Rumble is a realistic show as far as anime is concerned (no magical girls, demon hunters, robots, or ninjas), but it also strays from reality so often that the show doesn't even make any sense for the most part.
The basic storyline is a series of love triangles (and quadrangles) involving the main characters. Tenma (the hyperactive ditzy heroine) is in love with Karasuma (a quiet mysterious boy), Harima is in love with Tenma (the "hero" of the show and a delinquent), Tenma's close friend Eri (a rich girl and, to be honest, a real bitch) is in love with Harima, Yakumo (Tenma's younger sister, a quiet girl who can read people's surface thoughts...or something) who also likes Harima, and Hanai (a hotheaded martial arts expert) who is in love with Yakumo. There's also Mikoto (a friend of Tenma's and another martial artist) and Akira (another friend of Tenma's with little going on). There are other characters with less focus, though they also add to the love triangles, as if there weren't enough (another boy in love with Tenma, a girl in love with a boy who loves Mikoto, and some crazy Mexican wrestling girl).
For a girl who holds the interest of two guys (one of them obsessively), Tenma has no special qualities to speak of. In fact she has no redeeming qualities at all, really. She's unintelligent (which is a nice way of saying she's a moron), one of the worst older sisters I've ever seen, a ditz, a klutz, completely dense, mostly useless, very plain, and unfortunately meddlesome. At least she's a decent friend (in that she cares about them). It's hard to see what the other guys see in her, though to best honest Harima isn't exactly a catch himself. He's a delinquent, gets into fights all the time, has a short temper, jumps to conclusions easily, gets caught in way too many unfortunate situations, and fulfills his fantasies with Tenma by drawing them out in a comic book instead of growing a backbone and just confessing to her already.
The story in School Rumble follows these characters through their day-to-day lives. Mostly it deals with unrequited love, incomplete confessions, great misunderstandings, school functions (like festivals and field trips).... Well mostly Harima's attempts to convey his feelings to Tenma, and Tenma's attempts to gain Karasuma's attentions. The rest of the show sort of revolves around the consequences of the actions (or inactions) the two main characters perpetrate.
26 episodes and nothing freaking happens. Relationships don't progress, no one confesses anything, story lines don't wrap up. Things just get more ridiculous and more complicated. Which is why, I assume, there are 2 more seasons. Though there's no reason it couldn't all have been resolved in a single season considering all the useless stuff that's in there that wouldn't be missed if it was removed (meaning it wouldn't really affect the story). There's no way I could sit through 2 more seasons of this stuff though, so I have no idea what ends up happening to everyone. Although looking over it...the third season is unanimated? Except for a couple of OVA episodes, it seems.
I'm willing to believe that part of the reason I have such a great dislike for this show is that I was only able to watch it in English on the Funimation channel. Because they don't hard sub their shows for television (I don't mean the dialog but the kanji and hiragana onscreen), I miss out on a lot of the Japanese characters that are scattered frequently throughout the series (like the thoughts Yakumo sees, or random word bubbles). On top of that the English dubbing is considerably less than spectacular, specifically for Tenma. At least they left the songs in Japanese. If you're interested, Funimation is hosting some of the episodes (including the first 8 of S1) from the first and second seasons on their website. They started releasing the second season of School Rumble on DVD late last year.
As for me, I'll stick with Azumanga Daioh.