I feel like this is a pretty opinion based question, especially with IPAs being so "in" right now. Ignoring the taste of hoppiness, which is different from bitterness (dear Bob that myth needs to die), there's a limit to how much bitterness we humans can actually perceive. Past about 100 IBUs the tongue straight up can't tell that there are any more. Now we perceive the quality of bitterness differently.
So bitterness in beer is provided primarily by adding hops and boiling them for a long time. The length of time and pH of the wort affects a chemical reaction called "Isomerization", which is the process by which Alpha Acids in hop oils become Iso-Alpha Acids which stay stably in solution and make beer taste bitter.
Similarly, there are also Beta Acids. Generally these are in 1:1 ratio with the Alpha acids but sometimes there are more or less depending on the hop types.
Beta Acids are chemically Lupulones and Alpha Acids are Humulones. We've identified 3 types of each as well: No prefix, Co-, and Ad-. Most homebrewing hop packets list total alpha acid %, then % of those acids that are Cohumulone. But straight IBUs don't take which acids were used to get to that number.
Humulone is thought to give the best, smoothest, most pleasing bitterness. Cohumulone can be pretty abrasive, and the bitterness may seem rougher or more astringent...or just more bitter, even at the same IBUs. Beta acids are also thought of as a "rough" bitterness, but they primarily produce bitterness via oxidation and can help long term shelf-stability.
I don't know what all this really helps to answer, but I guess the main points are that you can't taste past 100 IBUs, but there are qualities to bitterness that can make some beers more abusive than others. Also my final point is that hop flavor and aroma don't make a beer bitter. If the hops have been boiled enough to actually make a beer that bitter...you do not taste those hops. You can have hoppy beers that are smooth and not bitter at all by hop selection, yeast selection, dry hopping, and not boiling them hops very much. You can also make beer more bitter by yeast selection and certain grains. You can also make Ruination or Palate Wrecker, but the point is that hoppiness and bitterness are not the same thing.