IXS is the most polished game of the bunch. It's tighter and less buggy than the others and has a lot more cohesiveness. It's easily my favorite. Just a whole lot of fun in general, great minigames or whatever they are called. Lots of stuff to do, things to collect, and island to explore. You get to skateboard against a skeleton!
LEGO Island has a lot of really neat stuff and the nostalgia is very strong for me but it's not nearly as much fun to play just for the sake of playing. It's fun because of the flavor, the music (good for all the games), and the nostalgia. It's the quirkiest of the bunch, without a doubt, and it is unique. I'd love to see a slightly more polished version but that won't ever happen.
LEGO Island 2 is a game that did a lot of things and did them about as well as is necessary for a children's game. There's a lot I love about it - sure, it's silly, kinda cringey at times, weird, and buggy, but there's a lot of good flavor. More interesting gameplay than LI, for obvious reasons. It's a fun adventure with a lot of really neat stuff all around you that captures a lot of themes from my early childhood (nostalgia is fun). And Ogel is just awesome. Sure, it'd be crap in any context other than this but within the context of LI2 it is perfect. It's a mess, but a glorious one.