I totally know the feeling of just suddenly being bored with a game. I think it's something that happens when you hit the point where you just know exactly what the rest of the game will be like. You simply have a sense that you've seen all the mechanics there are to the game, and simply doing more of the same isn't going to make a huge difference in how well you like it. All of the games you mentioned have sort of that flaw that they just don't have any systems where suddenly everything is different. You get a fundamental handle on all the relevant mechanics very early in the game and everything past that is just a laundry list of tasks you solve in pretty much the same way.
The irony is that games often end up being so bland because they were designed to be eternally interesting. Games that you're supposed to be able to put hundreds of hours into tend to avoid introducing new mechanics late in the game because if they have two hundred hours worth of side quests they don't want to hold anything back just in case you don't do the main storyline right away.
One game series I always really enjoyed was the Gothic and Risen games, and the biggest reason for that is because playing a mage in them is so much fun (especially Gothic 2). The spellcasting mechanics themselves are nothing special, what makes it interesting is that you tend to play through easily a third of the game without any notable spells before you are finally accepted as a mage and given the proper training. Since you need to get through a lot of harrowing adventures without the aid of magic you need to learn some regular fighting techniques first. You'll find yourself trying to strike a balance between preparing to be a mage and keeping your skills sharp enough to actually get there. When you finally become a mage in the second act of the game the majority of your skill points are still in martial talents, and you're starting to play catch up on the magic, getting it leveled. So in this act you're constantly relying on both skills, playing as a sort of battle mage who slowly gains power in the magical arts. By the time you hit the third act your magic talents have fully matured, and you're now a full on wizened spellslinger who can destroy any foe without resorting to vulgar forms of physical violence. That transformation your character undergoes is just really cool and keeps the game feeling fresh. The earlier titles also managed to end when you still wanted more, which is where I think a game should end. Some of the latter ones tried to add so much extra content that by the end you can also get bored just running around with a maxed out character checking off side quests.
Same, I main a healer myself. Though if I have to go dps, I play a BARD. I used to be part of a static but sadly we broke up due to big issues with the DPS 
