Sly was/is a brilliant filmmaker. A movie doesn't have to be "sophisticated" to be good... as indicated by the $$ success of the Rocky franchise.
As far as training sequences go, here's my list:
IV: can't beat the training montages, the contrast between Rocky working out in the barn and Drago using the "high-tech" equipment; the No Easy Way out scene is brilliant as well
II: love the old school methods... the sledgehammer in the junk lot, squats with the big log on his shoulders, chasing the chicken in the vacant lot, one-handed pull ups on the playground equipment
VI: bringing back some old-school philosophies with the kettlebells, squats, chains, smashing a beer keg, etc.
I: inspiring and classic, but training wise nothing special.