I've had a weird relationship with content in games. I felt ripped off after I'd bought Portal 2 - not because I didn't enjoy it (it was a fantastic game) but it took me ~ 7 hours to finish the single player and ~ 2 hours to finish the co-op, and I'd paid full price for it. That to me wasn't enough content to justify the purchase (especially since there was no real replayability other than going back and doing the same stuff again).
The biggest problem I'd have with paying full price for Titanfall, after seeing the reviews, is that there isn't a particularly large variety of modes. To compare the game to Call of Duty, while I do enjoy playing things like Team Deathmatch & Ground War in that game, what I enjoyed even more was Zombies (yes, Treyarch > Infinity Ward) and the smaller, weirder modes like Sticks & Stones; One in the Chamber and Gun Game. I'd say that about 70% of my time was spent across those 3 modes + zombies while about 30% of my time was spent in traditional game modes.
The reviews make out that Titanfall doesn't have any other incidental modes, nor does it have any form of co-op (and of course, a pretty sparse single player). There's nothing wrong with that, of course, but it wouldn't be enough to give me £40-45 worth of enjoyment and why I could never pay full price for a game like this.
Now maybe, like Portal 2, Titanfall would rectify this with lots of DLC modes down the line. But "down the line" I wouldn't be paying full price for the game, I could pick it up for a lot cheaper. So... yeah.