What ever happened to "role playing?"...
Well not sure but a lot of role playing could have occured during what you described. For example how did you "bluff" your way into the entry guard tower? Was it just a roll or did you role play it out with the DM?
Also when you were in your base camp thinking about scaling the cliff and apparently falling several times did discussion between the party members happen in character or OOC?
What it seems like though is that you are complaining about the overwhelming odds. First I'm surprised it wasn't a TPK! That was my first thoughts as you started to describe the numbers.
Now I would have to ask the question is were you sent to investigate the orc fort, retrieve someone/something from it, or to destroy it?
Throwing an no-win encounter is not always a bad thing, but leading upto it there should be signs. Just like the weather going bad without notice. You should have seen signs, especially the rangers. The party should know before that they are up against tough odds and the DM should give warnings to such.
For example, the ambush attack might have been a sign that these are above average orcs and well organized.
If you were sent to retrieve someone or something that again is a different story. Usually these are tougher encounters and the party is not expected to go in "full-force". Stealth was meant to be the "primary" way to solve the encounter, not that it should be the only way, but usally DM's have a primary way and one or more secondary ways. If you were scouting and/or retrieving someone/something then why did you kill the orcs? If you had gotten in, then I would have pressed it further.
As for the alarm, you said you were in the front guard room, was there a guard on the roof tower? All you need is one guard to hear and sure enough the logical thing would be to call all the guards/orcs.
Also, since this was your first sitting with the group, this may be the irregular. For example in my current group we have a mix of role playing and roll playing. Some nights are a single massive encounter, while other nights we won't have a single one, and will only make 4-5 rolls the entire 4 hour period. As others mentioned its how you like to play and how the DM likes to play. Maybe this was an "encounter" night?
Talk to the DM/group ask a bit more information before jumping ship.