Miss Berzerk Raccoon and I have been playing Lego Star Wars 2 recently, as you may already know if you read her blog. I own Lego Star Wars 1 and 2 and have finished all of the levels (a rare thing for me). I also recently bought Lego Batman after playing the Xbox Live demo, but haven't had a chance to play that yet due to the lack of a functioning Wii. So you could say I'm a fan of Travellers' Tales' (TT) Lego games. (I didn't get Lego Indiana Jones because I know a level designer at TT and he claimed the Batman game was better.)
Here are some observations on Lego Star Wars now that I'm playing through again in coop mode:
The inherent absurdity of a film license done in Lego allows TT to circumvent the restrictions of the license (especially this license: They can do things with Star Wars I can imagine few official Star Wars products being allowed to do). While you could do a funny game without Lego and you could probably even do a non-humorous Lego game, the humor and the Lego nicely reinforce each other.
Lego also means you can get away with simpler graphics and lower production values, which means lower costs as well as more platforms and thus more potential customers.
Lego Star Wars is made for replayability. It is easy to finish all of the levels, but advancing in the pretty deep metagame takes more time and skill. It also requires the player to completely break the rules of the Star Wars universe and replay levels with groups consisting of, say, Darth Vader, Han Solo, R2-D2, Jar-Jar Binks and young Anakin Skywalker, in order to reach each level's nooks and crannies. So this replayability is possible because of the light tone and irreverence regarding the license. Lego Star Wars' replayability would not fit in a Half-Life 2 or a Gears of War (although in the latter the replayability is in the multiplayer mode).
On a side note: This kind of replayability is an excellent way of generating more hours of fun per development dollar. A Lego Star Wars level might cost more than a similar level that is designed to be played only once, but it provides disproportionally more entertainment.
Lego Star Wars has strong casual game values: it's very easy to get into, restarts after failure are very quick, and the rewards are constant.
However, the game also proves again and again that being extremely forgiving and extremely charming can make up for a lot of mistakes, bugs and sources of frustration. And there really are a lot: fiddly vehicle sections, a camera implementation that means one player can push the other one off a cliff despite being on the other side of the screen, and very uneven level design. I actually find the game more frustrating during the second coop playthrough than during my first solo playthrough.
Despite that slowly increasing frustration, we're still having fun, and I can see us playing the game for a bit longer. At least, until my Wii works again and we can dive into Lego Batman.