Let's see. Reach is better than Halo 4 in the following ways:

- More gametypes
- More Custom options
- Campaign scoring
- No perks
- No random-ass ordnance system
- No rank-based weapon/ability unlocks
- Better HUD (it had a health bar, red X's, a compass, etc.)
- Better AI
- Various useful Forge tools (e.g. fine-tuned movement by clicking LS, zooming in while in Monitor mode)
- Better camera in Forge
- Forge World
- Theater for Campaign
- Less weapon redundancy
- Fewer visual retcons
- Mjolnir that looked like Mjolnir
- No QTEs
- Playable Elites in MP

Meanwhile, Halo 4 has the following improvements over Reach:

- Better weapon balance overall. It's still got its flaws — the DMR is still a tad OP, the Boltshot just needs to stop being a loadout weapon altogether (it should have been a low-tier ordnance weapon like the Needler), and there are too many redundant weapons — but for the most part it's good.
- Addition of object duplication, locking, magnets (though they are finicky), and trait zones in Forge
- ... Um... Hold on a second...
- Nope. That's it.

So yeah, Reach is a better game.