When you take the Undertaker into consideration, throw his career under the microscope, analyze it, you have to take things with the context of the times. Also, I'm going to right this knowing full well that people simply don't like or don't get the Undertaker. I understand that, it's like how I don't understand the appeal of the Rock, or why people insist on saying Jeff Hardy is good. I don't understand their appeal, so I understand people won't see things my way on the Deadman.
1990-early 1992.
The Western Mortician. The Original Deadman. The Undertaker was created to be exactly the opposite of Hulk Hogan. Hogan was all about bright colors, believing in the man upstairs, charisma, energy from the fans, dark tan, bleach blonde colorful guy. It worked, and to standards everyone is well aware of. The Undertaker comes along, the epitome of death. A man that was completely engrossed by the Darkside. It didn't matter how much light you had, or charisma, the Undertaker had a mystical power. You couldn't hurt him because he was dead, it was brillaint, and struck a chord with people. In his first year, I don't think he was terrible. He was slow, yes, but he was a zombie. The man wasn't going to have any technical classics. He feuded with an aging Snuka, which he buried at Mania, and had some Matches with Warrior, no major programs, but it says a lot in a rookie that they put him in feuds with Snuka, Warrior, and Ultimately Hulk Hogan. The Undertaker, a relative unknown, was the heel that managed to take the belt off of Hogan (arguably he was a part of ending two of his title reigns in 1991 due to the controversy of Tuesday in Texas). Bundy, Orndorff, Savage, DiBiase, Perfect, Piper, the list goes on and on. All guys that fell to Hogan and couldn't do what the Undertaker did. At this point, the Undertaker has become the attraction to replace Andre. The character was over, and he didn't need to grow as an in ring performer. He played the character, and played it well.
1992-1995:
As much as I like the Undertaker, this is the part where I have a hard time defending the man. However, I say that with this disclaimer, the WWE, especially 1995, was unbearable to watch. It was terrible, and in fact, I quit watching because it got so ridiculously bad. The Undertaker turned face, and the gimmick became over the top. The character shouldn't play to the crowd, and he did, and it didn't work. It wasn't bad until about 1995, when the Undertaker began addressing his fans as the "Creatures of the Night" it's cringe worthy. But, I don't blame the character, blame the booking.
The Undertaker had some shit feuds with guys like Kamala, Gonzalez, Bundy, "The Undertaker". So out of those guys, do you really expect the Deadman to have a good match? Those guys are terrible, absolutely terrible. He had good matches with Yokozuna in my opinion. A guy that he could actually have a good match with, he had good matches with.
1996-1998.
This is when the Undertaker grew, and grew tremendously. First of all, he started the year off with a tremendous match with Bret Hart at the Rumble. A solid 30 minute match which led to his feud with Diesel, and a good match at Wrestlemania. After that, the character grew. Mick Foley and Goldust are pretty much the names synomous with the Undertaker and 1996. As I said, you give the man someone good to work with, he'll do wonders for you. He had solid matches all throughout 1996 because he was actually given good people to work with, something he hadn't had to that point. I don't think it's a coincidence that his workrate and matches improved with the quality of the opponents he faced.
The Undertaker broke away from Paul Bearer, and finally the deadman was given a chance to shine solo. The Undertaker had arguably his best year in 1997. Contrary to popular belief, the Undertaker's title reign was a succesful draw. His title reign brought in higher numbers then Michaels and Harts reign. When the title was taken off him, it dropped. The Undertaker's title reign in 97 was fanfuckingtastic. Let's not forget, he had two good matches before his title reign. Vader at the Rumble, and the Final four with Hart, Austin and Vader. WM 13 was okay, but the confusion of that match took away from it in my opinion. Then he had an awesome match with Foley at Revenge of Taker, his best match with Austin at Cold Day in Hell, a good match with Simmons at King of the Ring, another Good match with Vader at Calgary Stampede. This leads to one of his best matches ever, another solid 30 minute match with Bret Hart. This was followed by two thirty minute affairs with Shawn Michaels, which led to the Hell in the Cell. Taker finished the year off with a good match against Jarrett.
So I'll continue this later, but I could write a book on the Undertaker. Prettty much, to sum things up. Taker is very capable of having good matches, it depends on the talent he works with. Do you really expect someone to get great matches out of Bundy, Kamala, Mark Henry, Giant Gonzalez and Great Khali? No one can.