Well, I got a good deal on GURPS Prime Directive (GPD) 3rd ed. at my favorite out-of-town game store.  I couldn't resist, so I bought it to get a little preview of what Prime Directive d20 (PD20) might look like.  I haven't read too much of it so far, but what I have read looks good.  
First, it is apparent to me that the people at ADB have developed (and possibly inherited) a great history of game development of the Star Fleet Universe (SFU) through the Star Fleet Battles (SFB) game.  GPD includes a page of publisher information that gives some of the history.  I found it a very nice touch.
The look of the GPD book itself is great.  I showed it to a friend who had only heard me talk of it.  His response was, "This is Star Trek!"  The cover is very evocative of the original series--a bonus or him if not completely for me.  I do think it looks great.  The interior layout is a very classic style of RPG books that I've been reading for the past 25 years, which I find appropriate since the same store had the new SFB Silver Anniversary rules on sale.  The interior pages are white with black text in a good font and density.  The illustrations are classic B&W, too.  
The book opens with a short story.  I find this a great touch.  It recounts the tale of a group of characters as they assemble and go through the introductory adventure delineated in the last chapter.  It was a fun read.  Hopefully, the adventure plays as well.
I'm just getting into the rest of the book.  Much of it is GURPS rules, so I'm skipping a lot of it.  I'm really only reading the flavor text.  I played GURPS a couple times in the past and more recently bought (and resold) the GURPS Hellboy book--I just don't get it enough to warrant reading a bunch of rules.  So, GPD probably won't be the game for me, but it does make PD20 look even more promising.  GPD has a short SFB chapter, so it might be worthwhile to get a little exposure to that game.  I'm also looking forward to reading the chapter on SFU; it has a galaxy hex map.