Castlevania 1 or The Legend of Zelda?
Bit of a sticker for me. I like both of the games a lot for completely different reasons. I'd probably go with CV1, though, since that's a game I can go back and infinitely replay and not get tired of it. Music is also better for me, and music is kind of a big deal to me in gaming, lol.
Simon's Quest or Adventure of Link?
Kinda weird choice since these games didn't come out the same year. Other games that actually came out in 1988 with Simon's Quest would be Altered Beast or Super Mario Bros. 2 (DDP), or even Super Mario Bros. 3.
That being said, Adventure of Link is easily the better game. It's like Simon's Quest but actually good. Simon's Quest has better music though.
Dracula's Curse or Super Mario Bros. 3?
Another weird one, since they're not the same year. Dragon Warrior, Super Mario Land, and Mega Man 2 all came out this year.
Dracula's Curse is easily the better game for me. Super Mario Bros. 3 is a masterpiece in its own right, being infinitely replayable and still holding its own even compared to modern games. But Dracula's Curse is my favorite NES game of all time. Game looks great, plays great, branching pathways, four playable characters, excellent music, multiple endings, intense boss fights. And its short and sweet enough to hop right back into after beating it.
Super Castlevania IV or A Link to the Past?
Another sticker for me, but for different reasons than CV1 vs. LoZ. Both of these games are just good to me, but nothing really memorable. I'll play them every once in a while, but I don't have any want or desire to jump back into them. They both look and play really nice, have great music, and are a lot of fun, but something about both of them kinda bores me time and again. This one's a pretty solid tie.
Rondo of Blood or Doom?
Rondo of Blood. Not counting the remake of it, RoB is the best of the Classicvanias, and like CV1 and 3, I'll replay this game over and over and over and still not be tired of it. I like Doom, but I've never had any desire to replay it after I beat it. They both have kickass soundtracks, too, though.
Dracula X or Final Fantasy VI?
Bust-a-Move, Front Mission, Panzer Dragoon, Twisted Metal, or Mortal Kombat 3 or something would've been a better comparison again, since same year.
But Final Fantasy VI, easily. Dracula X is decent, but from a technical standpoint, the game sucks. Overly repetitive environments, poor enemy placement, unfair hits due to short invincibility time you have, crappy level design, terrible final boss, etc. The Mode 7 flames look cool though and the music transitioned really well into the SNES.
FF6 is a fantastic RPG, though. There aren't many things I can think of that I don't like, and I certainly can't think of any off the top of my head.
The Adventure or Tetris?
Tetris. Game functions like it should and there's a reason it's been exactly the same since the 80's. The Adventure, while I find it decent, is a slow as molasses trod with some bad level design, enemy placement, and boss fights.
Belmont's Revenge or Metroid II?
Belmont's Revenge.
I've never played Metroid II, so BR wins by default.
Castlevania Legends or Pokemon Red/Blue?
Pokemon. Legends suffers from a lot of the same problems as The Adventure with some other wonky out of place crap. Pokemon is a classic, and while I personally hate the game series, there's no denying how solid it is.
Symphony of the Night or Super Mario 64?
Final Fantasy VII, Turok: Dinosaur Hunter, Tekken 3, Vandal Hearts, Star Fox 64, or GoldenEye 007 would've been a better comparison.
This is a bit of a sticker again, though. I love Symphony of the Night to death. Easily one of my favorite games of all time. I own it on literally every platform its come out on (aside from the Tiger Handheld), and I've beaten it countless times and still want to play it. But I feel the same way about Super Mario 64. Fantastic game and part of my childhood, so I also have some sentimental attachment to it. Bob-omb Battlefield's music never fails to make me excited. This one's a tie again.
Castlevania Chronicles or Majora's Mask?
Paper Mario, Final Fantasy X, Zelda Oracles, Conker's Bad Fur Day, Zone of the Enders, Twisted Metal: Black, and Sonic Adventure 2 all also came out in 2001.
But Majora's Mask. Both are fun games that I really enjoy, but there's just more going for Majora's Mask, and more bang for your buck.
Castlevania 64 or Ocarina of Time?
Honestly? Castlevania 64. I'm one of the many that just finds Ocarina of Time kind of boring after a while. Castlevania 64 may be kind of a wonky game, but I had fun with it, and its short enough to be fun for me.
Legacy of Darkness or Donkey Kong 64?
Legacy of Darkness. While I did play DK64 a lot as a kid, I honestly have zero memory of it. I still have my cartridge though, and once I get a new N64, I'm definitely gonna replay it.
Circle of the Moon or Mario Kart: Super Circuit?
Circle of the Moon. Mario Kart is boring single player.
Harmony of Dissonance or Pokemon Ruby/Sapphire?
Harmony of Dissonance. As I stated before, I don't like the Pokemon games, and this time its actually going up against a solid game, ugly visuals and wonky music aside.
Aria of Sorrow or Mother 1+2?
Aria of Sorrow wins by default, as I've never played any of the Mother games.
Lament of Innocence of Smash Melee?
Devil May Cry 2, Splinter Cell, Disaster Report, Xenosaga Ep. 1, Zone of the Enders 2, Wind Waker, and Ape Escape 2 all also came out in 2003.
But Lament of Innocence. Smash is boring single player and no one in my family or group of friends considers Melee to be the best (we're not competitive players). LoI is a solid game even with its hiccups and is one I replay frequently.
Curse of Darkness or F-Zero GX?
Minish Cap, Resident Evil 4, Oddworld: Stranger's Wrath, KOTOR 2, Tekken 5, Devil May Cry 3, and God of War all also released in 2005.
Curse of Darkness wins by default, though. I've never played any F-Zero games.
Dawn of Sorrow or Mario Kart DS?
Dawn of Sorrow, for the same reasons as Circle of the Moon.
Portrait of Ruin or Pokemon Diamond/Pearl?
Portrait of Ruin for the same reasons as Harmony of Dissonance.
Order of Ecclesia or Pokemon Platinum?
See above.
Harmony of Despair or Pokemon HeartGold/SoulSilver?
Never played the latter. So HD wins by default.
Pachislot or Castlevania IV?
I don't really get this one. I know it's just for fun, but most of us here haven't even played Pachislot, and the few of us who have would easily pick CV4 (aside from the few who honestly don't like CV4). It's just a strange one, like doing a comparison between Lara Croft: Relic Run and one of the modern Tomb Raider games.
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That aside, the reason I pointed out other games that came out the same year as the specified CV is because they just seem like they'd be a more relevant comparison, considering the year they came out. Like with Curse of Darkness, there are plenty of major releases in 2005 to compare it to that it just seems weird to compare it to something from 2003. I did notice you picked largely Nintendo titles to compare them too, but even in those situations there are plenty of Nintendo titles to choose from in the same year. I still answered them all, anyway.