Titanfall 2 is the best shooter I've played this year outside of Doom. I'm still not sure which I like more, but I've gone through Doom 3 times and have just barely started reaching the endpoint of Titanfall 2 -- been busy since it launched but been managing to sneak a bit of time here and there. Titanfall 2 helps in that I like its multiplayer as well, can't say the same for Doom.
... But all the factors seem stacked against Titanfall 2, so the sales not being fantastic in week 1 doesn't shock me at all. First, it is a problem that it was scheduled for release so close to Battlefield 1 and Call of Duty. That's insane to go up against, no less when Battlefield shares the same publisher. The tech test reaction, which is not a reaction at all that I shared (I liked it a lot) seemed to deter a lot of people, even people who had not even bothered to play the tech test. Combine that with relatively lukewarm long-term reception of the original Titanfall due to its multiplayer only focus and to me that seems like a storm for disaster. I came away from the tech test impressions thread knowing this game was very likely not to succeed, despite my own enjoyment of it. Seeing the really positive reviews and a dedicated thread about its campaign maybe had me hoping for a Doom style pickup in pace (which still needs more time to actually happen), but I think the fact that it's now the usual heavy-hitting fall/winter release season, that's seeing even more than just BF1 and COD coming out, kind of stacks against Titanfall 2's chances even more.
I still have hope this game ultimately succeeds, and despite the really good turn around it seemed Doom had in late spring/early summer (again, stressing that that was not a particularly heavy release season), I think Titanfall 2's up against some hard odds.