I am on the opposite side as well, I stopped playing Gran Turismo 5 completely.
I was quite pumped before the release of GT5. All those trailers, the pictures, the infos of the almost endless content. But when I bought the game and started my way through A-Spec, I just didn't feel at home. I thought this might be a temporary effect, and that the fun would come over time. But it didn't. I played my way though A-Spec (up to level 29) and B-Spec (up to level 25), but the game soon started to feel like a chore to me. I came to a dead halt when I unlocked the Formula GT championship. I only did the seasonals from then on, only for the payout. When that disappeared as well, I pretty much stopped playing completely. I did buy a couple of cars for fun, such as the McLaren F1. Had a great time in that for two days doing free runs and races, then it became boring to me (also because it turned out the gearbox is too long, an error on PD's side).
So I started to look what else is there. I stumbled over Test Drive Unlimited 2, and my PS3 hasn't seen the GT disc ever since I started playing TDU2.
The biggest problem I have with GT5 is that it doesn't speak to me. It doesn't urge me to play it. Before I moved over to TDU2, I came home from work, saw my PS3, thought of GT5, switched it on reluctantly and had B-Spec gather me some money. I can't even tell you why, I just did it. But I asked myself:"Why am I doing this?". At that moment, I knew I would start to look for fun elsewhere. Now, even before I am home, I am looking forward to play TDU2. It surely is a worse game in certain details, but the package as a whole is so much more attractive to me, which is the major key. I understand that a lot of people make the best of what GT5 has on offer, which is a great way to get along with the game. I however need a good overall experience. I remember sitting in front of my tv, watching a replay of GT5 and drooling at the incredible graphics. But at the end of the day, a few good things don't counter a load of bad things for me, which ruins the experience as a whole.
The game doesn't challenge me when I want to be challenged, the game doesn't reward me when I should be rewarded. It's not that I ran out of things to do in GT5, there are loads of things I haven't done yet. My problem is that I stopped wanting to do things in GT5. To me, GT5 feels like it slaps me on the hand all the time, forbidding me to do what I would like to do. There is a lot of content, but almost nothing seems finished to me. Where are Top Gear challenges? Why can't I do proper standing start laps on the TG test track against their leaderboard? Where's the Stig? Where are the reasonably priced cars? Where is proper Nascar racing (where the AI doesn't shove you off the track)? Where are proper WRC stages? Where is a proper Super GT championship with different classes on the track? Where is more depth in tuning? Where are more race modifications? These guys are Japanese - where is Touge racing?
All of this potential, just gone up in smoke. When I watch a GT5 trailer, it gives me the chills even now. It implies great things to be in this game. But they just aren't there. It's like the trailers show you a glimpse of an endless world, but when you get there, you notice that the world actually ends right behind the glimpse.
I haven't been playing GT5 ever since patch 1.07, and it never looked back since. I won't sell this game, and I'm not saying I will not ever give it another chance in the future. I've been a diehard Gran Turismo fan since part 1, and I don't give up so easily. But even if there will be a bootload of more patching, I don't really see anything that could get me to play this game for a longer period of time, simply because I don't believe they will be changing the structure of A-Spec and many more key aspects of the game on such a fundamental level that brings me to like it. But I have made my peace with GT5. It is what it is, and if it doesn't appeal to me, it's sad but true. I will keep looking at what they make of it, and I will be curious what and when GT6 will be. In the meantime however, I live in another world, and quite happily at that.