There are generally three reasons I don’t like certain secondary objectives; they’re too tedious, too limiting for deckbuilding, or too random.
1) Objectives which are too tedious
These are generally the worst, and most obvious to me; indeed they were the first candidate for attention back when I made this thread. IMO, these objectives should be avoided at all costs.
2) Objectives which are too limiting for deckbuilding
I think we’d all agree that some objectives which limit the cards you can play with and force you to find creative solutions during deck building can be fun, challenging, and keep the game fresh. However, some objectives limit your scope for deckbuilding waaay too much. Examples would include ‘Play X Eldrazi’ or ‘Play X Vehicles’. The problem here tends to lie in the fact that they rely on a very small subset of cards which are often underpowered, save for a couple of Mythics which few players have access to, particularly around the time of a new set release. The objectives are not limited to set specific creature types and mechanics, tho; try building a black deck for a ‘Finish with >100 life’ objective, and you’re either playing with Olivia, or with something much, much less powerful. Objectives like this often show up where there is a deficit of good card choices in the game e.g. life gain cards, or hexproof creatures.
3) Objectives which are too random
I prefer games with an element of randomness in them. Paper MTG of course contains a healthy dollop of both skill and luck, but these are not absolutes; the amount of skill and luck in a game are sliding scales. Puerto Rico is a good example of a game with a huge skill element and a very small luck element… but the luck elemtent is important to prevent the game from stagnating and becoming solvable. Some of the secondary objectives recently have included a little too much luck for my liking recently: in opening the right cards in boosters (see pt 2 above); getting the right cards and cascades at the right times during gameplay; and not facing an opponent who’s deck can interrupt what you’re doing. I’ve addressed a lot of my concerns about random objectives in this thread… they can be fun, and I don’t think they should be expunged outright from the game, but they can also limit deckbuilding, and they should not IMO be used as tiebreakers, especially if special prizes are being given away to the top players.
So what do I like? My favorite objectives are those that limit the number of creatures, or supports, or spells, you can play. An objective like ‘Cast 0 supports’ cuts down the cards available to you by 1/3, but crucially allows you to build the rest of your deck with the remaining 2/3 unhindered. ‘Cast <2 spells’ is equally as interesting, since you must rely on 2/3 of your collection, but you get the extra choice of deciding just how many spells you can get away with adding to your deck to make it better, and then you get additional choices to make during gameplay.
Let’s see some innovation in objectives like these! ‘Cast 0 cards that cost more than 10 mana’ maybe? Or ‘Cast <2 cards from Shadows Over Innistrad’? Or ‘Cast <2 colorless cards’?