I'll be doing ED next year on an X1. So here are my thoughts.
The X1 is not a 3 series, I'd descrbie it as a older equiped and liften 3 series wagon (which it really is) with fewer features and not as well executed vehicle. It's not as luxurious inside as a 3 series, more plastic and basic styling. You don't really get any features added to any bmw in the last 5 years. No powered trunk lift, no active cruise control, lane departure and collision warnings, the backup camera has a single camera vs other bmw's with multiple cameras/top down views, no active suspension for adjusting ride feeling.
The biggest thing to remember is the X1 has been out for 5 years in Europe and it's almost the only bmw model to not get redesigned or updated in the last couple years. 3 series and X3 just got updated this last year and both can offer far more features and refinement, and actually an X3's, depending on the options, are often only a couple thousand more than an X1, and still come with a few minor features with that difference.
I think the X1 sales would be much lower if the car had already been out for a year or two, but the new factor is what's helping it sell (and I'm sure there will be a lot of upset X1 owners when they see a completely new X1 "so soon" for the US in 2015 when it switches to the Countrman chasis)
The X1 is considered a baby or cheap bmw by some. I was at a local dealer the 2nd day it arrived in my area (in August) and two SA's just 15' away were openly mocking it while I was standing next to it (My SA was checking on something and not there at the time). The 2 SA's were basically going on how they couldn't believe bmw would release such a revolting and basic car and that they'd expect to see something like it from Subaru. I do though think that because of it's price and its fewer features than other current bmw's some snobby people will always look down on it.
However if you're not looking for every latest feature or styling and want decent older 3 series performance (and some people like the performance and handling of the older 3 series more than the new 3 series) that has some performance loss due to its higher ride height but find an X3 too tall and wobbly then the X1 is actually a good option. I have to admit it's a small market for this car. It's basically people who want to save some money and own a bmw and don't care about newer 3 series and x3 features. There's also a very small number of e90/e93 owners that don't want the new f chasis and are considering the X1 since it's the last e series chasis car being sold.
If Audi releases the q3 and when merc releases their gla next year bmw x1 sales will drop. Right now bmw has the only compact suv that has power and handling. Most people comparing cars are comparing to ones with less than 200hp or are actually outside the category of the X1.
Personally, I don't care about luxury gadgets. I'm getting a very basic xDrive35 for the power, moonroof, adaptive lights and adding cold weather and paddle shifters. No leather, no trim, just performance and that's why I don't mind the luxury shortfalls of the X1. The X1 is also within 2" on every dimension of my current car and I'm very fond of the height vs handling tradeoff. I also like the big hood style that most people don't, too me it's more old fashion. As for some features the X1 lacks, mainly lane departure and collision safety features, I'm buying the aftermarket MobileEye 560 that's the same hardware found in BMW, Ford, Merc, and several other manufacturers (they're really the only company in that market) for about $700. It won't vibrate the steering wheel or apply one sides brakes to bring you back into the lane but if you listen to the alerts instead of "feeling" them it's bascially the same thing. The only thing buying the Mobileeye doesn't do is really apply the brakes or auto dim your brights (though brights I believe can be retro fitted according to the docs) but in some cases the cars with MobileEye included doesn't apply brakes to avoid a collision but instead uses them to slow down the impact right before. I also see a benefit though it not having it capable of controlling brakes because an experienced and alert drive should be able to react to any warnings as well or better than software.