I wrote a bunch of stuff but then felt like I could sum it up a lot better in a few sentences, so here goes :P
I have previously used a 65" older model (2006/2007) 65" Mitsubishi DLP HDTV. However, the viewing distance and the content we used on the TV were never really optimum, and we never worried too much about stuff like "better get the 1080P rip of this movie". Everything was somewhere between "OK" and "great", but at 6 to 8 feet of viewing distance on a 65" display, you're not gonna see a big difference in 1080 vs 720.
I know there are image snobs out there who are like "OMG THE BLACKS NEED TO BE BLACKER!" and stuff, but I'm not one of those guys, so I don't feel super qualified to talk about picture quality in general.
I must say that owning a projector and using a 120" screen is pretty significantly different from owning a TV, even a "big" TV.
Biggest practical differences are:
-You gotta pay attention to your viewing conditions, and generally need it to be pretty dark in the room (which I was doing anyways)
-You gotta pay attention to your content, and will probably want to go for 1080P/highest quality versions of everything you do all the time.
The second one was a surprise to me even though it shouldn't be. When you're blowing up to such a giant picture, the difference between a 720P video and a 1080P video becomes somewhat apparent, even to non-imagephiles like myself. Also, I found that my attitude about content has changed. I guess my thinking is "Hey, I spent like $1100 on a projector and like $500 on surround sound, and like $100 on a screen, plus I have to keep the room just so and do all these things. If I'm doing all this because I want to get a big beautiful screen, I might as well put only the best looking stuff I possibly can get on that big beautiful screen."
The other thing is, I'm noticing that the "OMG ITS SO BIG!" effect is amazing for movies and TV shows. Like on the most recent episode of Doctor Who, there's a bit where they are floating in space through like an asteroid field around a glowing planet thing. That image in motion covering most of the wall and filling your field of vision is just like "HOLY CRAP!".
However, the same thing isn't actually always good for gaming. I believe this is down to the way games are designed. Essentially, most of the time you "need" to be able to see the whole screen, and when its big enough that you actually gotta rotate your eyes a bit to go from one corner to another, the resulting feeling is a little weird and off-putting. I haven't had a chance to play a lot of games, but both Injustice and Bit Trip Runner 2 felt a little weird. Since I presently just have my projector on the coffee table, I just scooted the table back, pushing my image size down a bit.
With a projector, you can do that!
I haven't yet played emulated games on my projector, and I'm really curious to see what its like to play like Nintendo 64 of SNES games on a big screen. I'll probably try that tonight and report results back ASAP.
Overall, I honestly can't imagine going back to a conventional television now that I have had it.
Its just too damned cool having what feels like your own personal movie theater, and pushing 1080P movies through it makes me giddy