If you are going for a specific achievement it is about 30% trial and error. Most of the time your plan will go accordingly, but sometimes, things will go south, and they'll go south quick.
If you're asking whether this is a guns blazing type of game, or a heavy stealth game like Deus Ex, it's honestly either or both. The game developers did an excellent job to cater toward anyone's play style. If you crave a good challenge, stealth might be your cup of tea. Super rewarding. Then again, combat can also be rewarding, too.
In many cases, taking out enemies quietly is far more effective then fighting them head-to-head. So props to anyone who can walk up to four enemies and wipe them all out.
In my case, I didn't want to kill anyone, but if that wasn't the case, there would be far, far, less reloading. You literally have an arsenal of options to handle any situation at your disposal.
The game developers knows there are people like me, so there is a quick save and quick reload feature: When you press start, you can hold R2 (quick save) or L2 (quick load) for about two seconds before jumping back to game play.
There were only a handful of times that I got annoyed. I want to say the game really opens up about Mission 5, when the levels become so much fun and there are so many different ways to tackle objectives and your character has upgraded several perks/skills.
That's when it really becomes fun.