I admittedly never got to play Halo 2 online, but Reach is just DMR: The Game. 343 even worsened that situation by making most playlists start you off with the DMR, and there’s never any reason to not have the DMR. It feels good, but it gets real old, and I played late in the game’s life cycle where half the maps in rotation were Forge World edits and all that gray really wears on you, especially since there’s only 6 maps for 4v4 otherwise (and nobody bought the DLC ones). I could believe that Reach is a better online game than 2 due to general technical improvement, for sure, but we’ll see when they’re both selectable in the MCC.
However, I played both their campaigns, and 2 has much tighter enemy placement and variety in settings, whereas Reach has many pointless first-person cutscenes and much dead space between fights (which also don’t really exploit the full space), and general Infinity Ward-wannabe limpness.