I feel like 1998 signified the beginning of the end of 90's greats. I mostly loved Hydro Thunder, Everquest, and Soul Calibur on my imported Dreamcast that year, but I don't think 1999 holds up as well, nor 2000. But we shall see!
Anyways, 1998 was still a fantastic year!
Some choice comments.
Metal Gear Solid - I think the game heralded truly stylish cinematic games. There were some cool FMV games like Under a Killing Moon, but MGS, while taking many inspirations, truly had its own style and themes. The game oozes atmosphere, which was beginning to become more rare by 1998.
Half-Life - I think probably the best Half Life game, I really love the industrial science theme of the environments.
The Legend of Zelda: Ocarina of Time - The game actually disappointed me slightly in the day, I wanted it to be more open with more towns mainly. The main body of the world feels empty and small compared to the detail of the 2D entries. But it was still great.
Thief: The Dark Project - Another one of the moody classics, such incredible style and gameplay.
Final Fantasy Tactics - I always thought FFT played a bit too slowly, but it does have the TBS chops for sure.
Pokemon Red/Blue - A classic. I played it in 1998 as a late teen but it was still pretty magical.
Banjo-Kazooie - What's with the moody, atmospheric games of this year? Here was have a cartoony game but places like Clanker's Cavern are just so thick with atmosphere. Probably the pinnacle of the collect-a-thon platformers.
Unreal - I think Unreal is pretty underrated today. The levels don't flow quite as well as Quake 2 nor Half Life's but it makes up for that lack in style. Definitely the best looking game of 1998 as well.
Mega Man Legends - <3 Tron Bonne
Panzer Dragoon Saga - Obviously legendary, but the actual game is truly fantastic. There aren't many RPGs that feel this rich yet cinematic.
Bonus "Hated It" section:
Shogo: Mobile Armor Division - Ugh, I was so hyped for this game, and when I saw the character models and art... What a massive turn off. Westerners really failed at mimicking anime style in the 90's. I mean people were TERRIBLE at it. These characters look completely amateur and pathetic. There is better art in asset-flip shovelware today.
StarCraft - I was such a graphics whore in 1998 I bought the game but sold it to a friend. I especially did not like the 'monkey'-looking Terrans. Reminded me of Blast Corps (which I enjoyed as a game), but I thought it was soooo ugly and technologically deficient at the time.