wait... you said rhythm/sampler int he topic. Then, GET THE ELECTRIBE S (ES-1), NOT the R model.
the S lets you sample your own sounds and sequence them. It is like a drumbox, but a"super" drukmbox basically. This machine has wonderful reviews. go for it man.
on the S, the sounds are YOURS so you sample the stuff you want (there are hundreds of audio CDs you can buy with hundreds of kits and breakbeats to sample!).
Add 64MB of ram on it though. After that you'll be unstoppable
Ahh.. by the way, I had the MC303 for YEARS (from the week it was out) and I recently gave it to a friend who graduated (nice present heh), he loves it, but I admit I had the same feeling as you, the drums are not that good.
see you around man