Well, it wasn't easy, but I scored a copy of this at 10:00 last night at Toys R Us. (TRU is the only place I know of that has it for $20--everybody else, at least online, is charging $30, and they don't have it on shelves anyway). Is it worth $30? I'm not sure. Is it worth $20? Definitely.
There's a choice between the slingshot control and classic control scheme (you can use the D-pad or the L and R buttons--the graphic is still a slingshot, however, not the classic aiming device). However, the slingshot control is so far and away superior to the controls of any prior version of Bust-A-Move that the button controls are pretty much unneccessary, except as a sop to purists. Most importantly, there's no more need to rock back and forth on the D-pad to fine tune your shot--it's totally instinctive now.
There's a puzzle mode that has 250 puzzles (five stages x five levels per stage x ten puzzles per level), with an unlockable "dark world" that has 250 more: I don't know if those are mirror images of the normal puzzles or what. There's an endless mode that's basically like Snood (yes, I know Snood came later than Bust-a-Move). There's multiplayer, but I haven't tried it.
The presentation stinks. The only way I know of to see a high score list is to let the game idle at the start screen, and it doesn't keep track of all the stats I'd like--just the time to beat levels in puzzle mode, and a single best score in Endless Mode.
So, yeah, it's worth $20, but good luck finding it.