So you've fired up Dishonored. Let's say you've never played Bioshock, Deus Ex, or Half Life 2. You'll miss the obvious influences that, at times, border on downright theft. Bioshock's art and storytelling style and "first person magic". Deus Ex's stealth trappings, pattern watching, and try-fail-reload-try-again gameplay. Half Life's eerily sparse cityscapes, and waves of masked soldiers.
The blend of borrowed elements from FPS classics leaves Dishonored feeling more like a mashup than a completely original experience. That said, great dishes come from great ingredients, and Dishonored certainly satisfies. I ended up choosing a stealthy playthrough, killing only when it was absolutely necessary (or a lot more fun), and I found myself frequently thrilled at my own success in evading guards and coming up with creative solutions to the mission's challenges.
This is really what kept me hooked - I couldn't wait to find the next mission's alternate routes and to try a new combination of powers and gear to get past defenses. The universe - an early twentieth century fictional Victorian empire, with puzzlingly advanced technology powered by whale oil - also drew me in.
My playthrough ended up around 16-18 hours, but it still felt a little short. I would have loved to see more side missions - there's typically only one during each main mission. And I'll agree with Patrick's comment that the game ended suddenly and without a conclusion that felt worthy of the somewhat predictable story.
Play this game if you enjoy any of its influences and you'll likely find it a pleasure as well. It's not as memorable as any of its predecessors but certainly a welcome addition to their ranks.