[The Fifth Horseman]

Frankly, what defines RPG genre for me is the freedom of choice and being able to affect the plot.

If Diablo was an RPG, you would be able to:
* Join the forces of evil and lead them against the world of men
* Do different things with items than required to complete the quests - and possibly that may prevent you from completing them. Like reading the "Fungal Tome" or eating the black mushrooms.
* Find a different way of lifting King Leoric's curse
* Wear a goatman skin and bullshit the goat-things (you know what I'm talking about) into believing you're one of them
* Refuse to help someone. Or demand compensation in return for your help. Or refuse to be compensated for it.
* Slaughter all of Tristram on a whim. Just because you feel like it.
* Find a love interest in Gillian. Or perhaps in Adria.
* Instead of solving the problem of the poisoned well by killing demons, solve it by collapsing the cave they're in.

And so on. The only quest in Diablo where you have any choice is the one with the tavern sign, where you can either bring it to Ogden and get a magic trinket or bring it to a pack of demons and be attacked by them in return. Where, I ask, is the option to cleave the pack's leader through the skull and proclaim yourself the boss?

Now, let's take Fallout.
You talk to Killian and take the job of bringing proof against Gizmo.
You can talk to Gizmo and take the job of assassinating Killian.
If you feel like it, you can also just kill them both.

You can refuse to save Tandi from the Raiders.
Or you can demand compensation for it.

You can defeat the Radscorpions by killing them all.
Or you can do it just by collapsing the entrance to their caves.

You can leave the Ghouls to die with no water supply.
Or you can help them repair their water pump.

And on the list goes.
CRPG is not the same as regular role-playing, of course, where your choices are literally unlimited. But the ability to choose and the fact you will have to deal with the outcome of your actions sooner or later matters a real damn lot.

Let's take a look at Arcanum now.

King Praetor, the King Of Dernholm asks you to retrieve the taxes from the Mayor Of Blackroot. Talking with Dante (a rather bitter priest in the Sour Barnacle), he will offer to assist you. You don’t actually need him to solve any of the quests.

Talking with the Mayor, he has decided for Blackroot to align with Tarant. You can convince him to rejoin Cumbria by :

# Showing him the newspaper article found in Dernholm and telling him of the dangers of being in the middle of the conflict.
# Pick pocketing the taxes and then telling him you have got them. By doing this you show him that the guards are incapable of protecting him and he decides to rejoin.
# Retrieving his ceremonial dagger from the thieves (these can be found west of the train station across the river). He will rejoin if you return the dagger to him. To do this you can

# Kill them all and take the dagger
# Steal the dagger from them
# Buy the dagger for 300 gold (depending on your skills this can be negotiated down to 150 gold)
# Procure some Poison from Grunwalde (telling him you are going to use it on some orcs). This costs 100 gold.
# Steal item from the Hedgewizard for them (this is a small shack in the southern outskirts of town). You can either steal the small statuette from the locked chest using thief skills or make a deal with the Hedgewizard to double-cross the thieves (he gives you a scroll of create undead to do so).

Returning to Dernholm, you can accept your reward. If you have Dante in your party, you can give him the credit for returning the taxes and he will then rejoin the king.

This is role-playing.

If it was Diablo,

King Praetor, the King Of Dernholm asks you to retrieve the taxes from the Mayor Of Blackroot.
Talking with the Mayor, he has decided for Blackroot to align with Tarant. You can convince him to rejoin Cumbria by :
# Retrieving his ceremonial dagger from the thieves (these can be found west of the train station across the river). He will rejoin if you return the dagger to him. To do this you can
# Kill them all and take the dagger