I love forging on Impact, it's such a nice new erm.. Forging field I guess you could call it. Adds more possibilities for map making themes instead of just the same old green everywhere or water all over the place... That's my opinion anyways...
Now the question of whether it is better than Reach's, in some ways, I find yes, in others, no. The magnets would have been a nice addition if not the fact they were implemented rather poorly for most pieces... The addition of trait zones and gravity volumes was also a very nice addition IMO. The thing that I dislike most about Halo 4's Forge though is that they kinda removed the precision forging, I mean sure there's the coordinates, but I never used those in Reach, I held down the thumbstick >.> with that removed it's much harder to get pieces the way I want if not using magnets D: