Yes, when my HDMI cable went missing, I couldn't play my PS3 for the week I had to wait to get a new one. The difference between 480i and 1080p is a galaxy's breadth. Games such as Armored Core 4 are nigh on unplayable as there are not enough pixels to fit the NEXT and the environment on screen, so you get to stare at the blurry hulk of a NEXT filling the screen, trying to navigate hopelessly using what little you can see over it's shoulder. Many will attest to the sharp, vivid and great ease of readability that HD bestows on text also. Additionally, my TV faces my window, and with a SD TV I couldn't play a game or watch a movie with the window open, lest I just want to see myself and the sky behind me. My HD TV has no glare to speak of, and dark is much easier to differentiate objects in, as well as being deeper (something I noticed immediately in Oblivion when I had to use a TORCH when I was in cave! Never had this been necessary before, even with brightness turned way down).
HD is far superior to SD when it comes to the games that it were developed along side it. Games that were developed to be played in SD vary. Some respond to upscaling well, and play in 16:9 nicely. Older games, particularly pre2002 games tend to suffer, things get stretch and look faded. Of course, you can get a good HDTV up to behave like an SD TV, so this is usually easily remedied. Of course these games don't benefit from the high quality textures, more complex character models employing modern modelling standards, different means of mapping, blah blah blah, so I don't expect they should look any better.
So when it comes to that which is supposed to be in HD, yes I cannot do without it.
