Bejeweled as a series is mostly about updating the graphics- Bejeweled, Bejeweled 2 and Bejeweled 3 are more or less the same Match3 game with tiny tweaks and prettier gems. Bejeewled Twist is the only game in the series that breaks some new ground, and it's well worth checking out.
On an 8x8 grid, you match gems by twisting a group of four, clockwise, so that three or more like-coloured gems line up. Those gems are removed, new gems drop into the grid, you score some points, and that's the basic premise. It doesn't get much simpler- everyone can pick up Bejeweled Twist and play a little.
Unlike classic Bejeweled, the game ensures that at each time, you have at least one possible move on your board. That's a generous gesture if you remember classic Bejeweled where running out of moves was an instant game over. But just because you always CAN make a move doesn't mean each game is endless. Par for the course you fill up a "progress meter" to advance in levels, and as you advance, all sorts of assorted nasty stuff is added. Locks make it impossible to move gems, and as they start to fill your grid your control over the board is heavily impacted. Bomb gems detonate after a couple of turns- you need to match them so they disappear. Should they trigger you get an increasingly smaller chance to still defuse them, but that's mostly based on Lady Luck and we all know you can't trust her. Simply put, the further you get the harder it gets to keep moving on.
A couple of neat mechanics improve your score. Each time you make a match a small counter goes up, eventually increasing a score multiplier. Max it out to 10 and you get a chance to trigger the insanely awesome, over the top Fruit Bonus (dancing fruit gems, anyone?). From Lvl 2 onwards, you get a Bonus Sequence of colours to match, filling up the multipliers a little faster. And just like the classic Bejeweled games you get to make matches of 4, 5 and 6 gems to create flame, lightning and hypergems, all of which are designed to clear up the grid more easily.
In terms of game modes Twist is a bit sparse. You get the classic mode where you try to surpass your highscore and a danger-free "relaxed game", which is the same without any nasty bomb stuff. There's also a timed mode, challenging you to get a high score in 2 minutes, which tends to run out of challenge quickly: There's only so much you can do with the mechanics and sooner than later you will have "maxed out" your score. A bit more interesting is the challenge mode, where a couple of different tasks in increasingly harder variants are available: This really is an interesting bonus and you may find some rulesheet there that really tickles your fancy.
But ultimately, the meat of the game is classic mode. Without time limit, with always calculated risk and a wide variety of valid tactivs this really IS the "Twist" game, and for the moderate price, any fan of Match3 should give it a try.