Apple TV was the only Apple device I've ever purchased that I was unimpressed with...so much so that I returned it. It's fantastic for certain things (especially streaming media from places like Netflix or iTunes), but I found it severely lacking in the mirroring department. I bought it to mirror from my Macbook onto my TV, and while it did some things decently while mirroring, playing media was a major let down (with constant lag on playback, sync issues at times and an overall degradation of the source). It seemed to struggle the most when trying to mirror 1080p files, regardless of type.
Truthfully, the Apple TV unit would be perfect if it allowed you to connect a hard drive to it, or if it could access network drives for film playback. Unfortunately, it has neither of those options.
At the end of the day, it really depends on what you plan to use it for...it has many strengths, including the specific apps available ON the unit itself...but in some ways, I feel it just doesn't quite function like I would expect. I have 2 Western Digital TV Live units in my house that mirror each other and stream files from a network drive as well as have access to Netflix and Hulu, etc. These were around $50/piece, and work MUCH better than Apple TV for what I needed.