I really thought the subscription model would be the normal way to pay for a console, the smartphone payment model. This would make even more sense with mid-generation upgrades.

I didn't expect PSVita to not even compete that well against 3DS, let alone mobile.

I didn't expect Splatoon to be such an amazing success story. Now there are doubts whether or not some of the most highly anticipated games such as FFXV, FFVII remake, DQXI, etc. are going to even surpass it's Japanese LT sales.

I didn't expect Xbox to have not as many exclusives this gen so far.

I didn't expect Cloud, Ryu, Pac-Man, Mega Man, and Bayonetta make it to Smash Bros. (though some of them were my dream picks).

Didn't expect the One to sell as relatively poorly compared to the PS4.

Didn't expect the Wii U to sell quite this badly (my 18-24 million estimate from 2013 has been shamed).

Didn't expect I'd be pouring hundreds of hours into FIFA again.

Didn't expect the Indie scene to be as fantastic as it has been.

Didn't expect The Witcher 3 to be as mind-blowingly amazing as it is.

Didn't expect Nintendo to wait quite as long releasing their next console.

Didn't expect spending so little money on gaming, despite the 7th gen being a disappointment in many ways.

Didn't expect I'd want an Xbox.

I didn't expect the Xbox one to be losing to ps4 in US (not just in sales)
I didn't expect so many games this time that on reveal looked great to turn out not so great (it seems a high percentage for me personally)
I didn't expect to move to Internet tv and love it (psvue is a service that exceeded my expectations which is rare)
I didn't expect to not own all recent consoles by now (there have not been break out titles to make me pull the trigger)
I didn't expect to see an NES remake official console and have to press my nose to screen to play it

I didn't expect Nintendo to push mobile as much as they're doing it.
I didn't expect the WiiU to undersell at this scale. My original prediction was 30-40m, and it didn't even reach half of that.
I didn't expect Pokemon Sun/Moon to be 3DS games, I thought Nintendo would push them to the NX to sell the system.
I didn't expect Fire Emblem Fates to be split into three games.
I didn't expect gamers would ignore the fees for the PS4's online multiplayer as much as they have.
I didn't expect consoles would go the incremental updates route like mobile phones did.
I didn't expect people would care whether a console has blue-ray reader or not.
I didn't expect Mighty Nº9 to be such a colossal dissapointment.

Didn't expect Wii U to be so disappointing
Didn't expect MS to fund something like Scalebound
Didn't expect there to be no exclusive Zelda
Didn't expect the resurgence of Japanese games on PS4

This one is interesting for me because I owned all 3 last gen and multiples of them: I bought 2 wiis and 5 Xbox 360s - I owned one PS3 given to me that I did not buy myself (first ever PlayStation and it was late in the generation)

One thing I liked about the PS3 was free online although I played online a lot more via my 360. 

The online price of ps4 vs PS3 was a complete nonfactor for me and MS mightily helped Sony in this regard.  I had in my mind to get two Xbox ones at launch and received a nasty gram from MS that I'd be paying a lot more for online coming up as they were ditching my family plan in favor of making me pay $60 * 4 per year!!  This email sat very wrong with me and actually got me to look into Sony more and their online service.  I already paid $50 a year for plus vs $100 for Live family plan. I found out my kid could be my sub on Plus for free and I could share my digital library via two ps4's between us for the same $50 a year.  MS, if I cut it down to just two logins, would be $120 and I was told I could not share my library except on one Xbox one (I realize people are doing it now but back then remember MS was going through a weird PR stage where every talking head said different things and at times seemed hostile to their customers - calling in to ask I was told they'd ban me if I tried it) so the decision was made easy.  

I could choose to pay half what I was currently paying on the new generation by swapping to Sony, maintain the same features and add digital sharing as an extra for that same price (a big factor for me this generation as couch coop is becoming less frequent likely because of wanting extra live/plus/console sales) or pay more to MS while getting less features I was interested in.

Long winded story but it's not always so black and white.  

I didn't expect the Wii U to be such a disappointment.
I didnt expect there would be no exclusive Zelda on the Wii U.
I didn't expect that I would buy a PSVita and love it as much as I do.
I didn't expect to regret buying a PS4 as much as I do.
I didn't expect to hate Pokemon X/Y as much as I do.
I didn't expect that Nintendo would ever go mobile.
I didn't expect to fall in love with Fire Emblem as much as I did this generation.

I didn't expect the PSVita to sell more than the Wii U.

I also didn't expect Bloodborne to turn me into a Souls fan.

I didn't expect the 3DS to do well.

I didn't expect Pokemon Go to blow up the way it did.

I didn't expect that my Wii U would collect dust.

I didn't expect Star Fox Zero to be as bad as it was.

I didn't expect to take advantage of the free PS+ games as much as I have.

Edit:

I somehow didn't expect No Man's Sky to be a disappointment.

I didn't expect Street Fighter 5 to get a Metacritic score lower than 85.

The original DS was way above the 100m units sold at that point, Nintendo would have wasted a giant oportunity not releasing it on the DS, specially when D/P sold the 3rd best in the series. And even then, Black/White was pushed alongside the 3DS for a long time, due to the 3DS being compatible with DS games (something we still don't know about the NX). Now, the 3DS has half of the DS installbase and their bussiness seem to be fusing their hardware division into one unified product/family. The NX needs the Pokemon push more than the 3DS needed it.