Probably not the best person to answer this question, because I checked out a few issues after Sienkiewicz came on (unlike most of comics fandom, apparently, I didn't think he was a good fit for the title).

Personally, I think if you're going to read any of it, you should just stick to the first stretch of issues from the graphic novel up to the point Sienkiewicz came on. To my mind, those best portrayed them as a bunch of confused teen X-men in training, and McLeod and then Sal Buscema drew the various characters so they actually looked like children/teenagers, rather than the way Sienkiewicz depicted them - where they looked liked twenty-somethings at best.

Outside of that, I later picked up some post-Sienkiewicz issues at random which I thought were ok, like the very special suicide issue (#45) and Annuals #2 & 3.

All that said, to your question of whether it was any good, I can't say I ever thought the series was anything beyond solid - I never enjoyed it nearly as much as the other stuff I was reading at the time.