Yeah, I spotted a LOT of copypasta in the Lost Mission, not least of all:
After all the speculation regarding the "new" final boss possibly being the previously omitted Spider Mastermind we all saw shots of back in the day, it ended up being the D3 Guardian with a (very slightly) different attack pattern.
That said, I still enjoyed it, and when you consider the fact that it's £25 for basically the Doom equivalent of the Orange box, it's not so bad.
PC-wise, I'd still recommend the original versions over the BFG Edition, though. The blink-and-you-miss load times don't make up for the rather questionable changes.