The Skeletal Legion isn't un-fun, but it sure does misfire in a bunch of ways.
This is the introduction to Commander Keegan's tomb. The players will find their way here from the Crypt of Shadows and arrive on the map above from the north. They're confronted with a corridor lined with "rows of sarcophagi", which connects to a large domed chapel dedicated to Bahamut, the Platinum Dragon (one of D&D's pantheon of "gods of good").
Naturally, the sarcophagi are a trap, and as soon as the players move between the first pair of coffins the whole set spring open and start coughing up magical skeletons. In the first round the trap spawns eight minions and two slightly-more-beefy warrior-types, and for each of the next five rounds it produces another two minions.
Clearly the intent here was that players would see this as a "never-ending torrent of skeletons", and attempt to escape to the chapel. Praying to Bahamut at either of the altars sends the undead back to their tombs, and thematically establishes the conflict between "goodness and light" and "foul, unnatural undead". However, it dosen't quite work like that.
First up, two minions a round isn't an "unending torrent"; in fact, it's barely an annoyance to a competent party. Twink-oriented groups will start farming for XP (at least until the trap runs out of juice), while even groups who aren't power-focused will get the clear impression that they are killing faster than the trap is spawning.
Secondly, the encounter is thematically confusing. These aren't just another bunch of the zombies that have been brought to life by Kalarel and the rift energies; they're a deliberately created magical trap, presumably intended to guard the chapel and the tomb. Why is a chapel to Bahamut guarded by undead? Who created the trap - was it here before Keegan went mad, and if so why? Was it installed afterwards, and if so by who? As we'll soon discover, the ghost of Keegan deserves some respect, but there's no evidence that "magical undead trap creation" is numbered amongst his post-death talents. (It's worth noting that if Kalarel had the power to spawn endless magical skeletons it would render much of his rift-opening work redundant.)
Thirdly, there's insufficient information. The players can't even see the chapel properly from the corridor, can't see the domed ceiling with the painting revealing who the chapel is dedicated to, and have no reason to think that praying at an altar would yield any substantive reward. (That's leaving aside the roleplaying issues of characters who might not feel comfortable praising Bahamut merely for the sake of convenience.)
And finally, it's a tactically uninteresting encounter. Even if you wanted to get to the altars, you can't, because the non-minion skeletons block your way. The exit, by contrast, remains wide open, so players just kind of bottleneck up in the entryway and settle in for some skeleton-killing. The skeletons have bows as well as their swords but as they don't have any allies who can tank and it's such a cramped space they really don't get much chance to use them.
Ultimately, smashing up skeletons never gets old, so it's a fun romp even if it doesn't work as intended.
 To make the encounter work as originally intended, move the tougher Skeleton Warriors to spawn behind the players, blocking their exit, and then double or triple the extra minions per round (to whatever you think your players can almost-but-not-quite handle). Emphasise the "silvery white light" suffusing the chapel area and play up the skeletons' unwillingness to go near the altars.