I'm playing the first Shadowrun. I'm playing as a mage, but I found a secret door in one level that requires decking to be unlocked. Now, I do have a decker in the party (I hired him exactly for this kind of situations) but it seems he's not really interested in helping me out.
Are followers meant to be totally useless outside of combat or am I missing something?

It actually depends of the checks. Sometimes you can use a follower to do a skill check (unlock a door, ...) sometimes you can't, it depends how they scripted it. It's a bit silly and I would like to be able to use follower skills always, but it also forces you to try different methods when playing with different skills, so it's not that bad.

Also, from my feeling, it's going better and better with the SR (you can do it more in DF than in DMS, and more in HK than in DF).

I see, so there's no way to know in advance. Thanks for the info, I guess I'll keep a decker in my party and wait for the time they'll prove themselves useful. It strikes me as a weird design choice, but whatever. I'm enjoying the game so far, even if it's much more linear than I expected.

It's entirely possible (you can make any skill check look for party member skills as well as your own), IIRC, but it depends on the level script writer allowing/implementing this. That's why it can be done in some cases, and not in others.

I agree that the game should be consistent; any check that reasonably could be done by a party member should realistically be enabled like this; if you take a skilled decker on a run,why wouldn't you let them do the decking stuff???

However I can also see the balance issue now that we have a regular "party" (not just random hired runners) who could pretty much fulfill any lower level skill checks without the player needing those skills, thus removing replay value ("next time I'll play a decker to see what was through that door") etc.

The first game, Dead Man Switch, is pretty linear. The two others (Dragonfall DC and Hong Kong) are much less linear, they have a main campaign which is quite linear, but lots of "side runs" you can do in any order or skip, and more ways to complete each mission/run.

You must be in the artifact liberation run.

Usually Gaichu can break that bookshelf down for you. One time I've had Duncan do it. I'm not sure what specific check you have, but I think it might be INT 5, maybe 3, and STR 5 or 6. I haven't been able to get Duncan to open it since. Racter may or may not do something as well. Is0bel and Gobbet however seem to rarely do anything.

Nope, Universal Brotherhood in the DMS campaign.

I ended up putting one point into decking just to activate the hacking option, and... it said my skill wasn't enough to open the door anyway, and suggested there might be another misterious way to open it.

I felt a bit trolled, then shrugged and moved on. =/

So, I've finished the campaign. Near the end I found another thing my decker couldn't be bothered to help me with. Two times in a whole playthrough, so that's not too bad; but on the other hand, I can't recall even a single time where a hired follower helped me with *anything*.
Likewise, I found that most of the dialogue options I had available lead to the same outcome. I don't really see myself doing another playthrough with such low replayability.

I really, really liked the settings though. Will try Dragonfall or HR at some point.