Yeah, I don't see how you can possibly find slaughtering endless hordes of monsters boring.
Diablo series and TQ just wouldn't be so much fun, if there wasn't tons of skills to learn/master and tons of loot to get. That's a major part of its appeal, I think.
About story-depth, I don't think we expect a Diablo or TQ to be on the level of say a Planescape, BG2, or The Witcher. Then again, what games really are?
If I was to suggest some action-RPG games w/ a better story, cool atmosphere, and has the crazy non-stop action and insane unique-loot dropping of say a Diablo; but also has some decisions to make when doing quests -- here's my own suggestion. I'd say to look at
Silverfall (Original) + Silverfall: Earth Awakening. I suggest you should only play these two w/ having both installed together. There's just too many technical issues by owning ONLY Silverfall: Original alone -- since the original edition is just not getting patched anymore; Silverfall: EA does fix a lot of issues with the original game (technical performance and a much much much better interface). Really, the USA needs to release that expansion pack and/or release a pack w/ both Silverfall plus SF: EA together.
Also,
Divine Divinity (if you can find it these days) is another pretty good for an action-heavy RPG like Diablo, too. The story is actually pretty good and the setting itself is pretty good. And yes, the questing has more depth to it than say Diablo's. One thing -- make sure you got the patch patch, b/c the game had a ton of bugs upon release; the game's in great condition now, w/ numerous bugs all cleared up. Another thing -- the voice-acting is all over the place. Some of it is bad, some of it is okay, some of it is good. With the game patched-up and all, the voice-acting is really the only weakness in the actual game itself now.
I've yet to finish
Beyond Divinity (which is also a hard find these days), but it is another pretty good action-RPG. Story's much darker and so is the atmosphere, when compared to Divine. Definitely action-packed, in the gameworld. The gameworld in Beyond is not as open-world style as Divine is, but it still gives you options and stuff when questing -- often, good vs. evil stuff. Plus, you control two characters here -- a character you create and an (Evil) Dark Knight forced upon you. Again, the same ordeal as Divine -- get the newest patch (this time, b/c it removes the StarForce CD check completely). And yes, unfortunately again, the voice-acting is all over the place.
Also, don't ever fucking lump Diablo 2 in with the shit pile that is Dungeon Siege. Those games are nothing alike on any but the most basic levels.
DS: Original + DS: LOA took what was great about Diablo -- ridiculous amounts of loot to get. It also took the Morrowind thing -- whatever skills you use, will improve. It also took what was great about Baldur's Gate series and Icewind Dale series -- full-party control, for big strategic battles.
It got all the basics right, gameplay-wise -- though unfortunately, DS never really had the atmosphere, character, style, plot, nor the presentation to catch up with Diablo series.
DS2 took a few steps forward (adding skills trees like Diablo II, adding somewhat of a plot, and somewhat better characters over the original), but also many steps back (the removal of the formation system, game does go on way too long, and an ending that leaves the player majorly hanging after 40 hours of playing).
Not really until DS2: Broken World did finally DS Series get things finally right, if you ask me (putting the party formation styles back in, a much more interesting plot, much more interesting atmosphere, more interesting NPC's, better banter, better presentation, some side quests give the player choices in how to finish a quest, and the game doesn't overstay its welcome). I'm sure many gamers felt it was TOO late to get it right w/ Broken World, but whatever -- it took Broken World expansion to finally get DS right.
And that's what gets me about DS3, w/ Taylor talking about removing the party entirely. I mean, Space Siege is a side-game in the Siege series that is in a sci-fi setting -- so, it's okay to toss the party out there; it's its own thing. Do they really need to obliterate the party for DS3? I mean, it'll probably basically become another Diablo game even more so, by tossing the party out. We don't need another Diablo -- that's what the hell Diablo is for. I always though DS was always about having a big band of adventurers to strategically slay stuff.
But yeah, the Diablo experience isn't necessarily readily apparent. You can't play it for a few hours and expect to understand why it has the longevity that it does, and why it's so much fun. You have to give it a good shot, and once you beat it and begin another game with the same character, you start to understand the cyclical, escalating nature of it, and why the challenges are so much fun to try and overcome. From what I've read, Titan Quest is kind of fun, but it's still a Diablo knock-off that doesn't really hold the same appeal, much less for the length of time Diablo can keep you enthralled.
I think TQ probably lacks the support of the MP-gamers and most importantly lacks Iron Lore supporting the MP with something like a Battle.net -- even more so, with Iron Lore gone now, obviously. I think most people play TQ to play solo, not MP. I never tried TQ's MP, b/c I want to finish SP first -- but I'm sure, I'll eventually try it out; hopefully, someone will be playing it on MP side of things!
While I think TQ is a fully 3D graphically prettier-looking Diablo II placed over a Greek Mythology setting, I think TQ has done the Diablo-style clone-thing better than anyone else.
I'd say that coop in these games does increase the fun factor, though. The original Diablo probably more so than Diablo 2 just because the first game wasn't as much fun in single player. A little too primitive and limited.
D1's SP was just okay. The MP on Battle.net was where that game really shined, that.
D2's SP is actually good and addictive. I'd expect its MP to be even better, myself -- since the D1 MP was very good.