Yeah, I loved ODST because it was a beautiful swan song for the Halo 3 version of the engine. It was like the DLC graphical bump multiplayer maps usually got, but for the first time, also for a campaign. Especially that last level on the highway. That sunset/flooded sky look, the carrier appearing in the clouds and then strafes the city... amazing. Then of course, dmiller had to top himself by having multiple carriers jump into New Alexandria and start glassing it in Reach :lol
But it really was the first time a Covenant capital ship actually INTERACTED with the world you were in. In Halo 1, there was one, but it was scenery (and seemed a bit.. underscaled from the outside). Halo 2 they were all painted into the skybox for most of the game and were barely noticeable in the first level as one flew by. ODST's glassing moment was so suprising because it was the first time one of them actually DID anything while you were playing.
Tsavo Highway in Halo 3, one blasts past overhead from behind about midway through the mission.
What got me at the end of ODST was the sheer scale of the carrier. It was the first time one of the Covenant ships had felt so truly, terrifying massive. I was just gobsmacked the first time I saw it; Bungie figured out how to convey the size of the carriers properly and it really had an impact.