These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Not so much when you have to re-fight it, though, as it now kicks up rocks from the ground which are not very easy to destroy in time.
Bustczar/Head Zeppelin is another example. ALL its attacks are destructible and cannot land a One-Hit Kill, and if you're good, it'll probably be able to use its carpet bomb attack only once. It's a breather because the previous two bosses and the next two bosses have One-Hit Kill moves.
Demonic Spiders: Havanski Atomic Bombers, they drop a large bomb that can not only take a lot of hits, but will instantly kill you (and your whole party, in War Party Survival) if it hits anywhere on the ground. For a large enemy, they also give you a measly 3000 points when defeated (as compared to the less deadly blimp that gives 25000).
Fridge Brilliance: You don't face any Havanski Atomic Bombers during both visits to Killingrad/Caliber City. The Red Star wouldn't want to nuke their main capital, after all.
Goddamned Bats: Most of the weaker enemies, especially Fighter planes when they are paired up with the blimps. Homing-missile helicopters are also really irritating too. Then there are ground-based Mooks like the rocket truck and the tank, both of which force you to aim downwards.
Barskov Munitions Blimps. They're big, tank damage for other enemies, and then there's the fact that they blow up into a random shower of indestructiblenote Unless you have the Nuke/Megalaser shots when killed and the shower may be impossible to avoid depending on the spacing between the shots. Thankfully there's usually a gap in the shower.
Fovraski Cruise Missiles. These fly in quickly, then do a 90-degree turn and head straight down when they go over a player. They are extremely fast, which means that you'll probably be forced to move left/right to avoid these guys or aim directly upwards to destroy them. And they always come in combination with Tachrok Ballistic Missiles, which limits your room to dodge.
Another enemy that appears alongside the Tachrok Ballistic Missiles is the Palinskat Ground Attack Fighter. They operate like Fovraski Cruise Missiles, but instead of dive-bombing you, they shoot a few energy orbs at you.
Goddamned Boss: X-Bot forces you to keep moving left and right to avoid his One-Hit Kill Stomping Attack. In the PC version, this makes it irritating to aim at him. And when you destroy both arms blocking the way, you also have to contend with dodging Eye Beams.
The Air Raid siren when Tachrok Ballistic Missiles are launched from the background.
It's the Same, so It Sucks: Both the level design and bosses. Each level has many different "waves", which consist of a set of enemies. Trouble is, you'll be eventually encountering the same few waves over and over again ad nauseum. And then there's the bosses. Bosses 10-18 are pretty much souped-up versions of the first 9 bosses, usually just faster and with more HP.
Scrappy Mechanic: In the PC version, your tank aims with the mouse cursor, AND moves towards the mouse cursor. This makes it hard to stay in one position and attack, and even worse when you have to face against Bulldozers that kill you on contact. Fortunately, it was solved in the PS3 and Xbox360 ports, with an analog stick for movement and the other for aiming/shooting.
Mechworm on the second fight. When his health gets low, it gains the ability to pop up under you. On the second fight, he pops out of the ground much faster, and if you don't move as soon as you see the Wormsign, you die almost immediately.
The Final Boss also counts, what with spamming of instant-death lasers that can curve around in its first phase, and instant-death nukes in the second. The third phase is by far the easiest... if you haven't lost your lives during the level or the first two phases.