The plot twist happens after 4-4, or is it 5-4 (helpings are fed to you before, a tad more heavily than in TTYD but whatever). The gameplay was good, but taking turn-based battles out drastically lowers the difficulty and I hated the flip time limit. Especially in that one corridor in Castle Bleck.
My opinion on Mario RPG goodness: PM:TTYD > M&L:SS > [SMRPG > SPM > M&L:PiT] > PM
The ones in brackets may move around inside occasionally. The others stand... this doesn't mean I don't like Paper Mario. I love all of the Mario RPGs. Paper Mario was just the least epic (really, Chup, have you played TTYD? Ever? What's wrong with it?).
The way I see it, go ahead and hate SPM. You provided reasons why. I'd suggest you finish it, though, unless you absolutely cannot stand it at all (...which is evident).
Toad... who DOES like Yoshi's Story? I mean, I used to, but I can't remember why.