Now, I'm not going to rip apart some poor horse for being poorly built, but I want to point out why some western pleasure horses move the way they do. It seems that breeding has been following a certain model, because the pleasure horses nowadays can so effortlessly four-beat and do all sorts of funny things with their legs. Their "bobblehead" necks are another odd pleasure horse thing as well. Have you ever watched a row of them going down the rail? It's hilarious. Unintentionally, of course, but I can't help but snicker a little as I watch a line of horses making some sort of soundwave with their necks.
Fast forward the above video to 3:12ish if you don't know what I mean. LOL!
Anyway, back on topic. I'm going to do an excellent, mediocre, poor, and extremely poor example (i.e., good, the bad, and the ugly, pretty much). Below is a very, very hard to find picture of a well-balanced western pleasure horse. In short, if this horse is a four-beater, his trainers met a lot of resistance to make that happen.
The horse above is a two year old, so he may be a hair downhill but I won't count that. He is compact, especially for a pleasure horse, because most of them resemble eighteen wheelers. His neck is turned toward the camera, but it is a nice width and length. His hindquarters are round and he isn't goose-rumped, a testament to both good breeding and training. He has nice, low set hocks, clean, proportionate legs, and although it's hard to tell, seems to have a decent shoulder angle. His head is proportionate to his body, and he has a kind, intelligent expression. My only bone to pick with this lovely young gelding are his hind legs--they seem a little camped under to my eye, but it might be the way he's posed. Not to mention the horse is in superb condition! He's not spectacular by far, but he is a huge improvement on most pleasure horses out there.

This is my "decent" pick. He, too, is compact, and is pretty darn proportionate. He has all of the attributes of the above horse, but he is goose-rumped and has wonky front legs. His hocks are set a bit high as well, and that might affect his performance a little. He's also a tad fine-boned in the front legs for my taste. I really like this horse in any case, and he would hold up very well for some un-intense pleasure. I like his head, expression, and nice clean throatlatch, too.
Above is his video, and I really like him. I dislike his lope (it's very jerky and does not "flow"), but he has the ability to have a slow-rollin', collected, comfortable rhythm to his gait. All in all, a decent horse, and still an improvement on most out there.

This is where things start to go downhill. (Get it??) This mare, although she looks very sweet, is just short of a conformational trainwreck--sadly, this is strangely ideal in the pleasure world. While she has a beautiful head and clean throatlatch, there are far more faults to outweigh these positive ones. Her neck is extremely long, and she has a telltale "dent" in front of her withers, which is a sign of her head being snatched up by force. It also appears to be upside-down, another sign of this same training method--basically instead of being encouraged to lift and arch her neck of her own accord, it is being held down in place. She is goose-rumped and far too fine-boned for my tastes. Her hocks are obscured by her tail, but they seem okay in placement. Basically this (very sweet-looking) mare will not be able to move faster than a slow crawl, but again, this is ideal in the industry.

On a side note, HOLY downhill, batman! This gelding is two, so technically he could catch up, but this particular farm has many mature horses who are built downhill. This is just an extreme case, but he is, of course, started under saddle and advertised as "an early futurity candidate for next year." Riiiight.

This horse is from the same farm as both of the preceding horses. He, too, is built downhill, and is as long as an eighteen wheeler. He probably has all of the agility of one, too. His neck IS actually shorter than his body, but it was a close call. He's got short, stumpy legs, high-set hocks, a goose rump, and a huge shoulder to drag the rest of his body around with. To his advantage, his color is pretty, and he might make some little girl the walk-jogger of her dreams, but he will probably end up winning the big classes. Why? Because four-beating, a low headset, and a slow, slow crawl will be second nature to him.
It's all discouraging, but the top two horses show a marked improvement on the last three--and most of the industry. Although, if someone wants to go beat the breeder of the last three with a clue-by-four, feel free. I'll be next in line.