Warning: Mammoth, rambling, unfocused post ahoy!
always complete games, unless there stupidly hard/dont like - currently churning through sleeping dogs, and completed farcry 3 before that.
the act of completing a game is easier than most people think and you can kinda churn through most games in less time then many online peps say. (bc they always overestimate!)
you just need to actually bother trying.
Someone earlier in the thread said "Why buy a game and not complete it? Surely that's wasting money" I'd just as soon counter "Why buy a game, then pressure yourself to rush through to the arbirtrary end point without actually thoroughly enjoying it? Surely that's wasting money"
Now obviously that varies by game, but I can't think of many games where the above approach of "churning through" the game doesn't end up being a lesser experience (in my eyes, obviously, I'm certainly not claiming this is true for everyone!).
I suppose it depends what it's being compared to. If it's 6 hours to spam through a game at full speed, see half the content, but complete the 'story' portion compared to 6 hours playing at your own pace, seeing all the content up to a point but stopping at halfway through because you lost interest, then I can see that the speed version gives a more 'complete' game.
In my case, the better comparison would probably be 6 hours of main story hammering, compared to 6 hourse of whimsical messing about, a two month break, another 30 minutes at random, another month's break, then at some point getting back into it for the remaining 10-12 hours and feeling it's been solidly completed.
Example:I recently picked back up Fallout New Vegas, originally started a year or two ago - my character now has all the companions, has finished the majority of the optional/side quests I've found, explored 90%+ of the map, 100% completed three of the DLC's and is partway through the 4th, and when he returns to the wasteland has the final "big decision" missions approaching rapidly. Now in order to 'complete' F:NV in my own estimation, I'd really have to do it three times over (minimum) with different character builds (intelligent gunslinger, stupid melee, evil energy weapons specialist etc) and different choices as there are multiple quests where you can only choose one branch, as well as a wide variety of endings. I'd also need to look at mods - there are HUNDREDS of amazing ones for NV, and I know people who'd consider not at least dabbling in them to mean you'd not got the most out of the game. For another person, looking up a min/max build online before starting, skipping all optional quests, clicking through all quest text/cutscenes, using fast travel whenever possible and making it to one possible ending would consider that 'finishing the game'. That's why most people would say Fallout New Vegas takes ~80-100 hours to complete, but if you know what you're doing you could see the end credits in probably 4-5 at most.
There are loads more examples. In Borderlands 2, I've done two playthroughs (main quest plus DLC) with a single character, but the game has five characters with at least three main builds each, plus I've not had a max-level character. Have I completed it? An additional DLC has come out since and I've not been back to it. Does that change whether it's complete?
I guess in order to try and address the OP's question (at long last) I'd say that a game is "complete" when I decide I'm not going back to it for long enough that I stick it in the 'inactive' steam category or uninstall it (PC) or put the box on a shelf rather than in the thing next to the TV (PS3). In that sense I reckon I've completed more than half the games I own.
Some (COD:MW2, BF:BC2, Arkham City, Assassin's Creed 2, Vice City, Fallout 3) that means not just completing the single player, but going through loads of the optional missions/achievements or doing loads of multiplayer.
Some it means finishing the story (usually the story led games like Portal 1+2, HL series, SpecOps the line, Borderlands 2 (for now) but also some action ones like Space Marine, Bastion, the Uncharted games, Fable series)
Some it means I've played them a LOT but just haven't put the time in to finish them, as in my New Vegas example, and will come back later (Skyrim, Mafia 2, Guild Wars 2)
Others I just got fed up with (Vanquish on PS3 - too willfuly confusing to really lose myself in. GTA 4 on PC - too horribly ported and grim to bother with. Street fighter 4 on PS3 - just didn't find I enjoyed it) - those I wouldn't call completed, but I'd happily say I'm unlikely to go back to them and therefore they are the only really 'uncompleted' category - the rest just aren't completed YET!
And still others will never, really, be totally 'completed' in my eyes (Titan Quest: Immortal Throne, Counter-Strike, WoW, Civilisation games, guitar hero type games, and I suspect Borderlands 2 may creep into this category over time)
) and love achievements. It gives an extra layer to games you really enjoy once you have finished the main story and pushes you to try something a bit different to the norm.
I finished Mafia 2 on the ps3 almost as soon as it was out (traded it in a week alter for fifa12) . Forgot to add it to the list, good game but it was done in 15 hours which was poor.
) etc. I wouldn't consider either type "bad value" in the £/hour stakes
