Thanks for your feedback

If you hold right click on an item in the loadout screen, it'll explain a bit of backstory and what it does as well. I am updating the wiki as well as I go - but essentially luck amulets increase the chance of enemies dropping things like health very marginally, as well as a very slim chance of saving you from damage. As the description says the effect is very minor but it's better than nothing. There's 3 more artifacts you can find - 2 in Millhaven and 1 in Providence (the Providence one is easy to find but the Millhaven ones are toughter)
I do agree about your points of the character abilities, they weren't implemented to the best that they could be. There's only a single time portal in the main episode, and it's part of a secret area. Merlijn and Zaxtor don't have a unique ability and Geoffrey's is hacking just like Mikkos. For episode 2 and future releases (maybe even a patch) adding more of these things is something I plan to do.
And I do agree about the bosses, although I found the Overlord to be a pushover since originally he was MUCH harder

The Robot Suit should never of fired that fast anyway so I'm doing some tweaking there...and again with the Entity I find him really really easy to defeat so it's always been hard for me to gauge it. The more easier I make him the less fun I found to fight him but other people's mileage have varied greatly.
And as for the secret, it's not signposted very well but if you head to the grey skull area and head up to the left skull switch, look around behind the switch (maybe take a step near the edge, see what you find)
EDIT: Heh, just saw your post Micky

There is one time portal in the main episode, in Dis Base. It's a very underutilized feature but I didn't want to use them in Snow just because it didn't seem appropriate. There WAS going to be a portal sequence in the Bunker map but I cut it when I realised making the player go back through the bunker again wasn't actually a fun idea. You can see a much cooler use of the Time portals in the map Urban Dead however. It's an invasion map but type map INVURB to play it since you can do it in singleplayer anyways (but just don't get infected!)