As for ODST, it was a bit on the short side, but I loved the story, and I replayed that campaign multiple times and gathered all the audio logs. Sure, perhaps it shouldn't have been full priced but I certainly got a lot of enjoyment from it. More so than other games I've purchased I'll tell you that.
I still maintain that ODST
being full-price was 100% justified (even if you had already purchased all of Halo 3
's multiplayer map packs).
The campaign was long (and different*!) enough and of a high enough quality to justify the price point, IMHO.