A few weeks ago I played a game of El Grande. (Thinking about a game that is called 'The Big' makes me giggle inside.)
I got blown out. I haven't played El Grande in a decade or so and I certainly didn't play perfectly so I can't say I am surprised that I lost. However, the game did illustrate one mechanic that I found frustrating. Oftentimes I try to figure out how I could change a game to avoid mechanics that bother me but in this case I think the mechanic is inherent to the game. The mechanic that troubles me here is the freedom to attack any player you want, without a clear way to figure out what you should try to accomplish with your attacks.
Early on in the game I was in a terrible spot. I got blown out by one spectacularly brutal card coming up at the absolute worst possible time, and I was dead last at 15 points while the leader was at 35. Not only that but she had far more units on the board than I did so I rated to get a lot less points on each scoring round thereafter. Given that my chance to win was vanishingly small at that point I decided that my new goal was to not come last.
Once my goal is to not come last, everything changes. Instead of trying to smash the leader, my optimal play is to punish the third and fourth place players, those just ahead of me. Of course those two players aren't going to like this conclusion as they would quite rather I attack the leader, giving them the best chance to win. But if I spend all my efforts attacking the leader then I rate to end the game in last place.
It is frustrating to be in last and to have to reevaluate your win condition, but it is just as frustrating to be in third and have the last place player clawing you down, gutting your chance to win. The key problem here is people don't agree on what your win condition is. If you don't agree on what you are trying to do, you aren't going to agree on what course of action is reasonable.
You might have a particular idea about how a player should play when and if they conclude that they are out of the running for the win, but there simply isn't any widespread agreement. Even then, players also have to be concerned about table presence. If a person attacks you to set you back, you can either ignore it or strike back. Retribution is often terrible in the game in which is occurs but its primary use is to build a table presence for later games. Who wants to go after the player who will strike back relentlessly, starting a cycle of mutually assured destruction?
There are ways to get around this problem. Some games just make it difficult or impossible to strike at a particular player. For example, Le Havre is a game in which attacking one player is possible but difficult. It doesn't suffer from this issue. Settlers on the other hand has the revenge problem all the time but because it is so random you can rarely conclude that you are completely out of the game. Even if you are behind it is quite plausible that you could run into a really fortuitous run of the dice and be back in contention, so going after the third place player is rarely a good choice.
One other way to deke around this problem is lack of information. In Castles of Mad Kin Ludwig you can see who is ahead on points but you don't know what cards people hold. This hole in your knowledge makes it far harder for you to figure out who is winning and also to be sure that you are actually losing. That sort of arrangement, alongside the fact that the game doesn't often present you the ability to smash particular people, means that you don't have that same problem of figuring out who you want to attack.
You can make it really hard to do anything to the opponents like Dominion does. Or you can obscure people's positions like Castles does. Or you can make the game really random so that everyone can always win and attacking the leader is always right.
However, none of those solutions can be easily implemented into El Grande. Even then, this isn't the sort of flaw that everyone sees as a flaw. Some people like always hitting the leader no matter what, or just having fun punishing people at random while cackling like a madman.
Any of those is fine, if that is what winds your clock.
But for me, I really like to know ahead of time what my goals are. I like to know what my opponent's goals are. I don't want to be in a situation where people will be going after completely different goals partway through the game and knowing that I will be a casualty of war. I also don't enjoy a game where partway through the leader is already determined and the rest of the group spends the game spiting each other, squabbling over second place because they have already given up.
It doesn't mean that El Grande is bad, but it does mean that it has a lot of potential to be really irritating, and I try to avoid games like that.