Lol I disagree about Trundle...his E and R are very good. Dat E, it is like Cataclysm and Crystallize, in that it counts as impassable terrain. Impassable terrain that slows enemies around it. Excellent for cutting off escapes, especially when combined with Contaminate. It also, iirc, will push people away from it a bit if they're near its center when it rises, so being able to separate is nice too.
And his R...weakening a tank or tanky DPS, making it harder for them to fulfill their role? Yes please! And then you just happen to get some of those stats for yourself, making you even better at your job.
I think the reason he isn't seen too often is...idk, I guess his price and his kit? The 4800 champs don't get too much love (it goes J4 > Rumble > Trundle > Orianna, in terms of popularity), and while Trundle is by no means a bad champ, he won't come off as sounding strong as much as champs like Nocturne, Udyr, and Lee Sin might. In other words, Trundle has a kit that is strong, but doesn't sound as strong as others. So in lower ELO you wouldn't see him much, but I'm pretty sure he's in the jungle in the higher ELOs (feel free to correct me if I'm wrong here).
On another note, is it bad that I have a strong urge to use Karma? I feel so dirty just typing her name...