The good replay value makes up for the rest.
What I find annoying are the infinitely spawning monsters such as Cephalos and Vespoids, it could have been better if they were finite. These monsters are not bosses, but require some skills to kill as they run a lot and can paralyze the player, which pisses me off when they almost instantly come out of nowhere and paralyzes you while you are fighting a boss monster (Vespoids flies very fast almost randomly and Cephalos can dig through sand faster than a man run through the surface and jumps out to attack the player with range and paralyze attacks) and some of the "hit-box" of the monsters; at times, I feel like the monster's range of attack seem to exceed the model of the boss monster as I get hit before the boss monster touches me, such as the hip-attack used by a boss monster named Plesioth, and due to the fact that these boss monsters come in a variety of sizes, the bigger they are, the even more range they have, so if the particular monster has a tail swipe attack, then you'd better run ahead before it uses it. And on the other hand, the melee attack range of the player seems to be smaller than the weapon he or she is holding at times, as I find myself trying to cut the tail off of an Elder Dragon boss monster.
Another thing I find annoying is that most of the time after a boss hits you sideways, you fall in front of the boss instead of falling to the side of the boss, which seemingly defies physics as to make the game biased so the boss can attack you again; if you fall side ways then you won't get attacked again as you stand up because by the time the boss turns towards you, you can roll away.
The annoying voices of the elder Pokke people are also something to abhor at. At times I would talk to the village elder of Pokke village, the village you live in, and the the missions open up for you to select, then the village elder starts talking, repeating gibberish over and over again as I browse through the missions, and boy is her voice annoying (they should have better voices for these elders).
In the end, the fun part is the game's ultimate replay value, and although it has no story-line and could have done better with a few things, this game will last longer than any PSP game you will own if you get addicted. With the help of the Xlink-kai and specific wireless USB adapter, the player can join with other players online and play together online even though the game is ad-hoc only, which is another thing I hate about the game, why couldn't it have been infrastructure? The game also allows you to transfer characters though the Monster Hunter PSP series so you can keep all the high rank equipments as you start on a different Monster Hunter game. Also, the equipment design in this game is awesome.
Personally, the game puts a lot of pressure on the player at times. You always want to do the right moves to prevent yourself from dying and at the same time maximize all the damage you can do to a boss monster so the time doesn't run out, and yes the missions are timed, a very long 50 minutes, but when fighting a monster you don't know how to kill, then 50 minutes might seem too little. Different bosses in this game require different strategies and you have to memorize their moves and respond with most efficient counter attacks. Some boss monsters are better finished off with specific weapons to save time, but the game has so many equipments that new players tend to be confused, but you can find guides of what weapons are best on the web.
If you like a game where you can collect cool equipments and has a long "life-span", then you probably won't regret buying this game. Also, it takes a few plays before the player can get absorbed into the game.