I've played a whole bunch of Diablo 3 since its release, which I partially legitimize as "research". There's a fair amount of gameplay overlap between what they're doing with Diablo, and what I'm hoping to pull off with Battleheart 2.
Like the original Battleheart, our next game is going to involve selecting from a pool of available powers to help you manage the battlefield. We're currently aiming to have nearly 100 different active abilities in Battleheart 2 (up from Battleheart's 50), many of which are coming over from the first game, with a whole slew of new ones too. These all provide different benefits like healing, single target damage, splash damage, defense, mobility, control, etc. Choosing your toolkit, and using that kit to stay alive is the heart of what makes Battleheart fun, and it's pretty much the same concept powering Diablo 3 as well. Across Diablo's five player classes exist an insane variety of powers and "runes" which modify those powers, sometimes into wholly different abilities. As you level up, you gain access to a broader and broader toolkit, and it's pretty fun to experiment with different combinations of offensive and defensive powers.
Where I think Diablo falls short is in it's difficulty curve, and the way it forces the player to use certain abilities and gear in a specific way. Around level 30 is the game's sweet spot - you have most of your toolkit available to you at that point, and you can freely use most of it without feeling obligated to play in any specific way. But afterwards, it steadily becomes more and more punishing as you approach it's hardest difficulty setting, "inferno" mode. Combat becomes so fast paced and brutal that you are forced to use several of your limited skill selections on defensive buttons and passive buffs. As a barbarian, for example, you simply have no hope of survival without relying on specific tactics - you MUST use a shield, you MUST use a defensive battle shout to raise your stats, and you MUST equip as much health and defense raising equipment as you can find, otherwise you'll be splattered like a fly on a windshield as soon as you run across your first foe.
To me, this totally pisses on what the whole game was building towards. I feel like I have very little freedom in how I build my character, because the enemies simply hit too hard and move too fast for any other tactical options to be available. It's really sad too, because earlier in the game the whole system is in full bloom, and you could freely experiment with different abilities and feel like you were refining your own unique playstyle. It works great, and then gets broken in an entirely avoidable way.
These observations haven't really changed how I'm approaching Battleheart 2, just reaffirmed what I've already been doing. Our combat is much slower than Diablo's, and you're never fighting huge unwieldy groups of 20+. This gives the player the time to parse what's actually happening and make decisions, rather than every engagement being over in the blink of an eye. We also don't have a ludicrous stat curve- in Diablo 3, you might start the game striking enemies for 10 damage, and be hitting for 100,000 damage by the end. A curve that steep will inevitably lead to rough patches where a little bad luck with loot drops will put you miserably far behind, or conversely, a little bit of good luck will trivialize hours of game play because you're doing twice the damage you're supposed to.
Overall, Diablo 3 has glimmers of greatness, where your gear level and the monsters difficulty meet at an ideal level, and your tactical options are at their peak, allowing you to feel powerful, challenged, and a little clever/creative with your character's build. I hope my next game captures some of that too. It just seems to me that Diablo is smothered by a few strange decisions, and held back a bit from its potential as a result.