Doodle Lab101 is a classic example of just what the App Store does best - physics based puzzlers. It's extraordinarily compelling and with just a bit more polish, it could be a true great.
There's a typically simple concept behind play - you have to direct various balls (or elements) into their respective beakers. This is done by drawing lines with your finger so as to create barriers that force the balls in the direction you want. It's not as simple as that, of course. There's only a set number of balls that you can fail to save, for example. Different colored balls react differently with some being heavy and desperate to drop down, while others bounce happily and unpredictably around the arena.
Some of the levels are easy to figure out what you need to do next to navigate the balls in the right direction. Others are a bit more fiddly and take some thought. Oddly, there doesn't seem to be a natural learning curve to this. Simple levels are interspersed with difficult levels so it's not obvious that levels will get increasingly harder the further you progress.
Annoyingly, Doodle Lab101 also offers an utterly useless tutorial which you're better off avoiding and figuring it out as you go along. Fortunately, the game is very simple to learn with only occasional moments of trial and error required. Another annoyance lies with the touch controls. They're not as accurate as they should be. Instead, wherever your finger is placed, the cursor is a few centimetres away. Once you get used to this, it's fine, but at first it can be rather frustrating.
It's a shame to see such problems, as Doodle Lab101 is great fun. Offering 70 levels with 30 more promised soon by the developer, and also GameCenter and OpenFeint support, Doodle Lab101 is a complete package of physics based puzzle fun at an ideal price.