I have been rummaging through the monolith for a couple of weeks now. My initial impressions....
The core rules are a tool-box. What you use will be based on your style of play (if you are actually playing a campaign). If you are not actually engaged in a Traveller campaign, there is a lot here to amuse you.
If you are a gearhead - your prayers have been answered. If you are not a lot of this is, well, worthless. I am a role-player, not a roll-player, therefore vast swaths of the core rules are useless, for me.
If you loved T4 - T5 builds on that. If you like Classic Traveller, Megatraveller, or god forbid, TNE - a lot of this will be jarringly unfamiliar, and won't make a lot of sense at first.
In my opinion, the level of granularity that Marc added is just more paperwork for things that will only be used once, if at all. The KISS principle isn't something that Marc appears to believe in.
Too many of these rules if "provided to the players" will send them running for the doors.
On the other hand, if you are a shitty GM with no imagination and an inability to think on your feet, you do have a solution for almost any problem (as long as you don't mind constantly flipping through the monolith to find it, because there is no index).
I see a lot of clever solutions to problems I have never once asked or had a member of any group ask in the past 30+ years of playing Traveller. Perhaps I have been playing Traveller the wrong way all this time.
The Flux concept - I play Traveller, not Yahtzee - not to mention that it gives the player too much information.
Genetics - what problem does this solve? If I want characteristics to dominate over skills, I'd play D&D. This is what actually drew me away from D&D to Traveller.
The Senses - see genetics.
Gunmaker, Blademaker, Armormaker, etc. I suspect that 75% of this will be used once, if at all. On the other hand, which 25% is used will vary from group to group. In my case, the first 3 won't be used at all - Thingmaker, perhaps. As a role-player, it doesn't matter 1 whit if I shoot someone with a rifle with a 5.56mm or a 7.62mm, they are going down.
The artwork. 70's line art doesn't cut it. The sad part is a number of the folks who made art for Traveller back in the day are heavily engaged in making 3d art - go visit the Traveller groups over at deviantart.com You will see several familiar names.
If you are not familiar with Traveller, don't bother. One of the book's core assumptions is that you are intimately familiar with Traveller and it's past.
T5 is NOT designed to bring new players to the fold. Much like Total War (the remake of Fire in the East) it appears to be geared to long time gearheads. I am sure the sewing circle is happy that their vision won out, I am ambivalent about it. I would have preferred seeing a simple, clean game system that would entice new people to the game system, as opposed to a placating a bunch of whiny grognards. I haven't seen anything that T5 does better than CT or MT - more complexity, but not better playability.
I figure most people will add the rules they like to their preferred game engine and ignore the other 500 pages (which 100 or so pages will be different for every group, depending on playing style).
There are several sections that are definitely going to move into my version of the MT rules, but T5 as a whole, meh.