SW3 is really amazing. Its just as easy as the previous games but the production is f*cking lush. Its one of the best Sega games ever, IMO. SW4 is more like an add-on disk. Its super super short (I think there are two battles) but it has an ending for every girl in the series, which is...a lot. I can't remember.
The best part about it is something Yoneda says in the ending that, IMO, encapsulated Sega at that point. Something about flowers blooming for only a short time or something like that. ST4 was the last Sega produced game for one of their own consoles (Puyo Fever came later, inexplicably, but SW4 was supposed to be the last) and for all we knew it would be the last SW game. Yoneda's statement seemed to be talking about the death of Sega, right when I was playing their last real game...got me a bit misty eyed, if I'm honest.