Like the last two covers of the Dungeon Masters Guide, the fourth one -- for the revised 2e books, sometimes called 2.5e -- was painted by Jeff Easley.
I can only assume that the art director of this revision gave explicit instructions to Mr Easley to go with a "breaking down doors" theme. It's the only explanation I can come up with as to why both this cover and the cover of the revised Players Handbook both illustrate a group of characters busting down a door in a dungeon.
I'll give this cover points for including a dungeon, but that's about the only good thing I can say about it. Easley is not one of my favorite D&D artists by a long shot; he's not even my favorite 2e era artist. Even so, some of his earlier work is good, if not necessarily old school. His later art, though, strikes me as ... cartoonish. Perhaps that's not the word I'm looking for. In any case, the three creatures bursting through the dungeon door here -- Ogres? Hill giants? -- simply don't look real to me. They have an almost stylized character to them that's made worse by the shading and coloration of the piece. They look, as I said, like cartoon characters rather than like something appropriate for a D&D illustration.
More to the point, what exactly do these ogres have to do with the Dungeon Masters Guide? Had this been the cover of, say, the Monster Manual, it might be a bit more appropriate, but the DMG? The illustration reveals nothing about the content of the book on whose cover it rests. It's just a generic piece, devoid of both context and meaning. I understand that some people don't mind covers that don't really "connect" to the content, particularly when dealing with things like referee's manuals; I'm not one of them. For me, referee-oriented books already have enough strikes against them as it is. There's no point in making them even more unattractive to buyers by giving them covers that are so uninspired and unrelated to their purpose.
All in all, I think I can safely say, with even looking at the 2.5e Monster Manual, that this iteration of Dungeons & Dragons has by far and away the worst cover art of them all. I simply have no idea what TSR was thinking when they commissioned these pieces, but then it's quite likely, given subsequent events, that neither did TSR.