I’m currently playing through the ODST Heroic playlist. ODST is just how I remember it, with one noticeable exception. Every time I start a level with the Rookie, my weapons reset. This means that every time I return to Mombasa Streets after completing an “action” mission, as well as when I start Data Hive and Coastal Highway, I start with an M6C/SOCOM, an M7S SMG and a pair of frag grenades, regardless of what I was carrying previously.
It takes me out of the game to suddenly have my weapons change on me, and it makes it far more difficult in some places; for example, fighting your way back from ONI Alpha Site without a sniper rifle.
Hopefully this is a glitch that can be fixed, and not an unavoidable side-effect of integrating ODST into the Collection.