I was insanely psyched for Reach...I waited at midnight, played it all night with my roommate after he got it, and then went and got my own copy the next day.  The first week I was loving it and finding it hard to divide my time between campaign and multiplayer.  But after I beat the campaign on heroic, and started going back on Legendary, I started losing interest.  Then I realized how much less fun I have playing mulitplayer without another friend in the room.  Thus Reach popped out of the xbox, and hasn't been back since the first week.  Anyone else have this sense of blase towards the game, or can you think of any other examples where the things weren't as great as they seemed after a little bit

Mass effect 2, at one moment something clicked when I was on the normandy 2.0 about 30 hours in and I lost all interest in playing the game anymore.

Yeah, it all went downhill after I got tired of seeing jet packs. I also realized that Halo online multi-player gets my blood boiling more than any other game by an astronomical amount when things go wrong. 
 
Don't get me wrong, still a great game but I can't play it for very long without wanting to punch babies.

That is what happens to me and basically all games.  I can't understand how anyone is able to play the same game night after night like some people are.
 
I put in Reach just last night, but I probably didn't play it as heavily as you did.  (but I did solo Legendary)
 
Looking at your achievements I did play more than you did of Reach...  But I would still say never expect any game to absolutely entertain you for a very long time.

This actually happened to me in Fallout 3.  I turned it back on after not playing for a while and continued a mission.  I tried to pick up something and realized my pack was full and I would have to leave the area and go back to Megaton to sell everything.  Instead I just turned it off.

Happened to me after a month or two of MW2, I thought the same thing happened with BC2 but I put it in today and still really enjoyed it so I'll be playing that more often. 
 
Dead Rising, Red Faction: Guerilla, Split/Second, and Prototype are some significant ones I can think of that I just lost all interest in at one point and found something else to do/play.

sounds like you should play this one with your roommate or another friend. Some times even passing the controller is more fun than playing alone.

happened to me with mw2. 

I still play it, but definitely not as much as I did the 1st week

The only example of that I can think of is MW2, but I still had lots of fun with it and I wish I could still play it now (I sold it).  Boredom for online games that I enjoy almost never happens in a permanent fashion.  I've been playing SSFIV frequently since it came out earlier this year, for example.

" Mass effect 2, at one moment something clicked when I was on the normandy and I lost all interest in played the game anymore. "

I didn't play it all last week but am again going strong

" Mass effect 2, at one moment something clicked when I was on the normandy and I lost all interest in played the game anymore. "

I've never really been able to play many shooters for over a month. I'll go back and play some of them, and I'll say I wont get rid of X because I'll want to play it later, but I just don't. Got rid of MW2 after maybe a month only doing maybe 2 missions single player and all the rest in multiplayer, sold CoD4 after a week without touching the campaign . I seem to hold onto Halos a lot longer though, mainly cause of fond LAN memories on Halo 2 in my friends attic. 

" @LiquidPrince: Probably. "