LSW:TCS is crazy addictive, endlessly entrancing and the massive amount of content makes it well worth your cash.
The Complete Saga is just that...all 6 Star Wars movies crammed into one really long Star Wars adventure. You play through Lego Star Wars and Lego Star Wars II and along the way you collect numerous hidden objects which all lead to other un-lockable and purchasable items. This formula has been used a lot in gaming and Traveler's Tales hit the nail on the head with LSW:TCS. With all of the collectibles tide into the achievements system, this game gets addictive really quickly. Obviously I didn't play it on any other system, but I can't imagine myself playing through the levels numerous times if no overlying is given like on the Xbox 360 (no achievements or trophies in the PS3 and Wii versions)
Aside from a few minor changes, the gameplay is identical to that of it's source material. All of the platform stereotypes are here. The number of un-lockable characters is amazing and with the levels set up to force replay you end up learning a lot about the characters that you've unlocked. You learn who exactly in the SW universe are bounty hunters vs those that are Jedi. The game is still mad easy, but this time it feels like you are accomplishing something by replaying each level.
Also, the first LSW was ungodly short, and I never played LSW2, but after playing them both in the same game, more time can care was put into the later. The Original Trilogy levels are much longer and in some cases required harder puzzles and tasks. Nothing in either game is too terribly difficult, but with both of them strung together, you feel like whatever amount of money you spent on the this game was well worth it.
I ended the game with about 860 achievement points, before finally saying "dude, I am not putting anymore time into the freakin' game". I suggest anyone that is remotely interested in Lego and/or Star Wars pick up this game and start slashing away. It's also great for kids and the numerous side quests and additional content makes it well worth your time. I would stay away from the online features, but you really can't go wrong with Lego Star Wars: The Complete Saga.