I'm extremely lazy and I don't want to read all the thread. Askin' very simple questions:
1) Is the basic game decent? I play a lot of Megamek but sometimes you want variety. With "decent" I mean "enjoyable", I understand this shit ain't perfect. I just want to see robbits burn and I don't care about SJW stuff (we already had fucking Canopus and the Clans, can't be worse)
I think the best part is kitting out mechs since you have a pretty decent amount of options for that, including the ability to strip or add armor. I remember I stripped armor from some definitely too light for the job mech to fit in some overkill weapons setup like 2xAC20 or something else for the premium glass cannon experience. Who needs armor when you can do called shots crippling shit from really long range.
The tactical combat isn't particularly deep, it suffers from nu-xcom-itis adopting its "move+shoot or sprint" system. Melee is pretty much just a special attack with 1 range that also fires small weapons, with no additional mechanics such as attack of opportunity or whatever to give it additional tactical meaning. This means there's nothing stopping the other guy from walking behind you and alpha striking you.
Due to the retarded cap on the number of mechs deployed, light mechs are obsolete pretty much as soon as you get anything heavier. Stability damage was nice until story and random missions have you facing heavy or assault mechs, making stability damage-focused mech loadouts not really worth it at that point. Evasion is ok as a mechanic.
There is some decent use of terrain and environments (planets) impact heat management differently, so there kind of is some thought required to picking the mechs for the job sometimes besides what has the most mass and thus dakka. Furthermore terrain height and line of sight do matter.
In general the tactical part can be summed up as wasted potential. It is ok, but honestly you get the feeling more could be done and it does get repetitive.
Mechwarrior skill development is too simplistic and results in low variety between mechwarriors and not much room for specializations. I honestly had a lot more fun in the tactical area with nuXCOM and its sequel, make of that what you will. Mostly because nuXCOM introduced new tactical options as you progressed while here, not so much. Just gear with some better stats, with the exception of the new mechs I guess.
The lance management strategy side is passable as is the ship upgrading, not bad from what I remember, just mechanically inoffensive and thus forgettable. Choosing the salvage to cash ratio is kind of fun, but the salvage is heavily RNG-dependent despite employing tactics to maximize available mech parts. I really wanted to get some endgame mech parts and the RNG kept shafting me despite employing tactics to maximize available mech parts.
I got bored of the random missions eventually as while the tactical side is ok-ish (mostly due to the mech loadout options), it just gets repetitive and there's not much too look forward, despite some improvements in the random scenarios brought in by the DLC. It just feels like more of the same. Thus I couldn't be arsed to finish the game and I honestly don't know if I'll ever bother, there's just nothing motivating me to see the end of the campaign or even the flashpoint content, neither storywise or gameplay wise.
It doesn't help that going from system to system takes so fucking long, with so many animations which cannot be skipped. Also it runs like shit for who knows what reason, urban maps especially. And it loads so fucking slow. I would blame it on Unity but even compared to other Unity games (Wasteland 3 for example) it runs and loads fucking slow, period.
No clue about mods.
General recommendation - wait for a price cut and at least a 66% discount if you really are thinking of buying it. It also has the issue of being a typical paradox game where you can swear the DLC should have been in the base game in the first place, but they are nickel and diming you, because paradox. Also no kickstarter backer discount for DLC is a dick move.