They're very different. Persona 1 and Persona 2 have the emotions element, and actions picked stay consistent unless a random dialogue prompt changes it for that battle. If one action provokes the reaction you want, it will always provoke that reaction. You can see this in the guide that Arue linked, which shows specific reactions that always provoke joy.
In contrast, the mainline SMT system doesn't use emotions, and is more like a standard dialogue wheel. While each demon has specific personality traits in regards to what they like and don't like, actions are not always consistent, and doing the same thing will not always produce the same results. SMT4 in particular is especially tricky, thanks to the wide variety of demons and conversations they have. I know one big mistake that beginners in SMT4 make is giving in to every demon's demand, when a lot of demon's actually prefer it if you know when to not give in and end the conversation.
I actually prefer the standard SMT negotiation system over the one used in Persona 1/2. While it wasn't too bad in Persona 1 when successful conversations got you a Spell/Persona card every time, it became downright annoying in Persona 2 when you had to provoke the same reaction several times just to get one Persona.
I actually don't mind the emotion thing as a gauge of how well you're doing in a negotiation, since that was sort of my beef in SMT4, but after getting told the, oh what was it, the rule was like "give once or twice, end negotiation, repeat till success" thing, which worked out well enough most of the time, I did find it much less painful. The real difference or clincher was that SMT4 had a Compendium, meaning I didn't have to acquire new demons if I didn't want to. I could just keep buying old ones and fusing them in new ways, which is precisely what I did for most of the game.
P1 is sort of different from P2, though, in that doing the same action does in fact provoke different responses, and I never feel like there's enough leeway to really try to find a new "good" response before it all goes topsy turvy on me.
If we really want to talk about something unfun, not reliable and not well designed, we could talk about P3 and P4's dungeons.
What didn't you like about the SMT IV system? It's waaaaayyy better than the randomly generated grindy non sense that P3/P4 gives you. It's not that bad in Persona because the games don't have fully customizable parties and you hardly need to fuse in P4(black frost nukes the game and I used Orpheus up untilfor P3P) but that kind of non sense in a game with 400 demons? LOL.(I'm assuming you don't find the random persona mechanic in P3/P4 unfun, unreliable and not well designed)hanged man
1. I actually don't think I can name an RPG where I felt dungeon design was good. I can name some where I think it was bad, but I don't know that I've ever felt like one was particularly stellar.
2. Which random element of grindyness are we talking about? I feel like this is something obvious and I'm just not remembering it. Maybe I would change my position if somebody stopped assuming I was intelligent and told me what we're talking about?