Yes, it was the first pistol I shot, and I haven't shot many others, so I'm a little biased. Since I don't have much experience with other pistols, I probably don't know what I'm missing. I've hated the Glock's that I have shot. All of which were owned by law enforcement officers, but I don't know if they had a particular "LEM" trigger.
The "Law Enforcement Module" is a replacement firing mechanism for the HK pistol that changes it from a standard Single/double or double/single action (depending on your choice of carry) to a modified single action. The hammer's cocked when you chamber a round, but there is a disconnect between the hammer and the hammer spring. There is no external safety, the safety is the trigger just like on a glock. If the trigger is not manipulated, the connecting bar from the trigger to the firing mechanism will not actuate the firing pin block. That firing pin block is spring loaded and always in position on all the USP pistols unless the trigger is manipulated. The advantage of the LEM is that like with a Glock "safe trigger" or whatever they call it, you have a repeatable, consistant trigger every time you pull the trigger. There is very little if any discernible difference between your initial trigger pull from the draw, and the trigger pull from firing... ie, you fire, release to trigger reset, and fire again... and you aren't going to have much if any difference. However, unlike a glock, a LEM trigger module is capable of double-action firing if necessary due to whatever reason. Having the double action is nice if you're doing reloading with new primers that you haven't tested before... if it takes double hammer strikes for say 2-3 out of a pack of primers, you know you should just shoot what you loaded, and either A: mark the rounds you load with that batch of primers as training ammo only, or B: just toss those primers and shoot what you have left from that reloading batch.
Basically, you give up an external safety and decock capability for having less to have to manipulate. It is something you can buy for any USP model, but I don't know if they do the same for the new P2000 or whatever the hell HK is selling these days. USP's are a big pistol, larger than comfortable for most people.. but like it says under my name, I'm not nicknamed sasquatch by some on here just because of my looks, I'm one big mofugger and the doublestack .45 fits my hands just fine. Never mind that I can conceal it with day to day clothing without any issues, and even in the lighter clothing required to survive summer in the south I still had no issues with concealment.
Of course, there's the anomaly of my wife who is 5'5" and who actually prefer's my expert to her compact due to the expert's trigger vs her compact's trigger. She has no issues with manipulating anything on either of those pistols, nor any issues with firing accuracy or speed of follow up shots.
I haven't bothered with an actual round count for my Expert, but just going off of how much we'd reload and shoot 4 days a week back at Ft. Benning between myself and the wife, I have put at least 60,000 rounds through it and it is still going completely strong. I would call up the wife during lunch at work, and have her crank out a thousand or so rounds and we'd shoot them all between the two of us when I was released for the day. Daytime, Nighttime, Summertime, Wintertime. Four days a week. Every week. Usually I would end up burning more of the rounds since the missus would get bored or would start coming up with new scenarios for me to shoot.
Now, I'm restricted due to finances to doing dryfire only for any sort of training. My concession to that is every time I get up and put my pistol on I do 50 draws and dry-fire engagements with whatever I'm wearing to go out and about just because... so I do what I can. I'm not willing to dip into my oh-shit reserve to continue to train with live fire.
The most major reason I prefer the LEM is pretty simple. Glocks are not comfortable with their grip angle, and in general I just don't like them. The LEM brings the "Glock Safe action" effectively to a weapons platform I prefer, have trained on, am comfortable with, and above all (as mentioned above), have a slight bit of proficiency with.
The USP .40 pistol I first bought was a nice pistol and at that point I had no specific brand orientation... if I had the money, I would buy some FN P.45 Tactical's because they fit even better than the USP, and have a higher round capacity capability in the .45 caliber. Price with HK's is a huge deal, considering that a new Tactical or Expert is going to buy you 2 or 3 other pistols.