I'd actually forgotten how much I loved Invasion in Reach. It was basically all I played. The Needle rifle was actually superior to the DMR on smaller maps when they both had bloom, because you could get more shots off quickly before the reticule went to shit; it gave the elites at least some hope of not getting completely crushed.
I think the main reason I enjoyed Invasion really was because once you got a sniper as a Spartan the Elites were pretty easy to pop in the face, and you could power weapon hog on Boneyard so much that it was hard not to get at least a frenzy every game.
I have to say though that the tiers felt really good in Invasion and Boneyard and Spire had very different feels to them in terms of gameplay - which I see as a big achievement -and it was impressive that both respective defenders felt more powerful simply due to map design (high ground advantage, weapon spawns etc.) rather than the armour abilities they were wielding. Although having said that, armour lock/shotgun combo on Boneyard in the third tier was a pain in the balls.
As with most Halos though, I never got to play the DLC map(s?) for Invasion because they never seemed to be in rotation or the playlist was totally empty.
Hopefully dedicated servers will mean that we actually get to play DLC maps now, rather than having empty playlists for months and feeling like we all wasted our money.
tl:dr - Bring back Invasion, make DLC work properly (we got dedis now).