Mega Man
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I've played through the first 3 games, but I don't like the embellishments they were starting to add by then. I prefer the simple mechanics of the first 2 games.
In terms of characterization/personality/whatever - I liked this simple also. You Mega Man! Go - Kill Bad Guy!
Even the robot dog thing in MM3 is a regression IMO from the mechanical gadgets you get in the first 2 games. They were trying to add personality but I just found it silly. Mega Man being equipped with his own mechanical gadgets is an idea I like a lot better.
As years went by in the age of the "X" series games the series was turning into an anime cartoon with superfluous characters and unnecessary dialog and storylines. I don't need that stuff and don't care for it, but I could ignore it if not for the gameplay that I also just don't find as enjoyable as the early games.
Zelda
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I never got into the 3D games. I played Ocarina of Time way late and wasn't impressed, but I'll try it again sometime if I ever get my cartridge back. I also played Majora's Mask but didn't get very far.
I've played Breath of the Wild a few times. I like it but it doesn't hold my interest for very long. What happened to the dungeons? The simple "temples" or whatever they're called feel like dessert, they can't be the meat of the game.
My favorite thing to do in traditional Zelda was overworld exploration and you can certainly do that in Wild, but I think top-down Zelda was more fun to explore than the 3D perspective.
Constantly breaking weapons are annoying. Exact opposite complaint I have with Bethesda, who stupidly got rid of that feature entirely from their games.
Fallout
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I haven't played enough of this series to count it but I'm mentioning it anyway. I never played Fallout 1 or 2 (I want to). I started with Fallout 3 which I really enjoyed. I know it's unpopular with the F1-2 fans, and I can see how in terms of lore Fallout 3 would be grating. Since it was the game I started with I didn't really notice and just enjoyed the atmosphere and gameplay.
I was in a pretty negative mindset at the time, particularly with respect to the BS of the political world, so that probably helped me to take some sick pleasure in the setting of Fallout 3 where all political constructs are obsolete rubble. I've heard people say it's depressing, and I agree it is, I just didn't mind.
The gameplay of that game has some faults but I found it very entertaining. The silliness worked for me with that game.
They're the same gameplay mechanics that I *dislike* in Elder Scrolls (Oblivion/Skyrim). Maybe that's the bias of liking whatever version of a game that you played first, but I also think this gameplay style works better for Fallout than it does with medieval fantasy. Especially the combat, which I find infuriating in Skyrim but I enjoy it in Fallout 3. It works better with guns than it does with swords.
Now that I know more about the history, I do think the factions in Fallout 3 are too one-dimensional with obvious "good guys" and "bad guys".
I have New Vegas, haven't done much in it yet but I've already seen playthroughs of that game. It looks good. The western desert is where I'd want to live in real life, so I think I can dig that, but the radio guy sucks.
I've watched a partial playthrough of Fallout 4 and have no interest. I don't care about the setting, I don't see that it adds anything compelling vs F3-NV, and I really hate that they got rid of item durability. How can you put a game in a post apocalyptic survival setting and then fill the world with perfect unbreakable equipment? If you find one copy of a weapon you're set for the rest of the game. The whole concept of scrounging around for scrap to turn a few broken pieces of junk into one less broken piece of junk has been lost. I find that outrageous.
Elder Scrolls
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I'm on the fence about TES6 - I'll look at it whenever it exists, but feel the series has declined. The peak for me is TES3 Morrowind, which was also the last TES game that was designed primarily for PCs and the last that I'd call a traditional RPG.
When Bethesda consolized Elder Scrolls and Fallout, they changed both series from traditional RPGs into hack and slash adventure games. They're a different genre now.
Presumably this is because console players using a game controller on their couch don't like the same slow pacing or complexity as PC gamers traditionally did. I'm no different - as much as I love Morrowind I'd never want to play it on an XBox. But that doesn't mean I want TES to change to cater to the XBox. That's what happened though, because that's where the money is.
Skyrim's leveling flattens the difficulty of the world to ensure you can go anywhere. The irony of this is that it makes it feel like exploration doesn't matter anymore. Everywhere you go will have the same stuff. Every cave will have the same random loot, the enemies will be the same, it just doesn't matter. It hurts the sense of adventure.
Skyrim tries too hard to throw quests at you. I've got so many in my journal I don't even remember most of them, and have no sense of caring about them. They're generally just "follow the quest marker" instructions.
If you pass an NPC on the sidewalk they start announcing their personal life drama and yell "Talk to me! I've got a quest!" It's a far cry from the conversations in Ultima 6, that's for sure.
Not that Fallout 3's NPC are any better. I know they're not, I just didn't care as much. The "Mr Burke" encounter at the start of F3 has to be the most ludicrous thing I've ever seen in a game. Not what he's asking you to do - the jarring way he goes about asking it. Bethesda needs to have some patience and let the player decide what nooks and crevices of society they want to explore, get immersed in, and build a rapport with. Not just throw stuff at you randomly.
Bethesda seems to have a poor opinion of the player and tries to backseat drive you through their games.
Skyrim's invincible items is a shared complaint with Fallout 4, but it irks me slightly less in the TES setting. I think it's weird that Bethesda invested a lot of effort trying to make blacksmiths interesting in this game, but at the same time they changed the mechanics so that they're useless. Buying their equipment is unnecessary because you can get that stuff everywhere in the wilderness, perfect condition, and it all fits you. Nothing needs repair.
The only thing blacksmiths are good for in Skyrim is to buy your excess loot. They're not blacksmiths, they're financiers.
If I was to mod Skyrim this is an area I'd like to improve, but I think it would not be feasible within the features that exist in the game engine.
When TES6 comes along there's a chance I drop out. But... it's hard for me to totally give up on it.