If I'm playing a hard game like Castlevania III, I'll always purposely game over at the start of a level if I'm below the amount of lives you start with, so I can get some extra chances at the level. I'll also whip every wall I can find just in case there's a pot roast hiding behind it.

Everything must be explored unless it's a huge pain due to some annoying game mechanic. Also, I don't like stuff laying around, so if I can collect it, I will.

I explore everything in open world games. And I feel very uncomfortable having lots of side quests to do, so I just do them. I'm very compulsive about that.

Manual saving. If I just cleared some ridicules section. And I can control how often I save. I'll start saving a lot of times. Just to be really sure.

That's the worst way possible to play Fire Emblem the way I see it. A strong/otherwise valuable character just died honorably? Let's restart the chapter to make sure he or she survives and keeps the party at peak strength.

No chapter resets, on the other hand, means you always have to consider every decision carefully, and actually risk not being able to complete the game if you're not competent enough or can't deal with the deaths of certain characters. If you're up for the challenge, I'd highly recommend it.

OT: As time goes by I find that I'm having less and less OCD habits dragging my gameplay experience down. I, too, used to pick up unnecessary heart pieces and rupees back in the day. In shooters I'd use up whatever ammo is laying around unless the process would be too time consuming, while in F-Zero I would try to kill all enemy racers when possible regardless of their score and expected performance, resulting in many unnecessary SD's on more dangerous courses.

Whatever is left now always at least serves some form of purpose, like making sure that my weapons are reloaded, all enemies in the area are dead, friendly units have the best availale gear, no valuable loot is left behind, all conveniently available collectibles are collected, etc.

Who are you to tell how to play my games. 

Respectable though. I could never handle character deaths, really. Especially in the endgame where the character is simply "retired"... :/

Nothing like getting all the collectibles (unless it's a Skyrim type game) however once I start a game I HAVE to finish it and generally I won't start another game until I've finished the first one.

The need to collect trophies on PS games, and I've gotten to the point where I hate them. Collecting them all is so time consuming, but I feel an urge that I need to collect them all.

Also, in RPGs, I feel the need to collect everything in an area. I find it hard to move on if I haven't everything in a dungeon, field or town.