Excellent space opera. The special effects are so good in its work on world-building, and characterization is very well done. All the characters are so greatly introduced and developed its like the modern day Star Wars (1977). It manages to deliver the great action scenes and thrills, and humor is consistent through the movie. They combine to deliver an original that is fresh and captivating.
There are a few plot holes and problems though. What is the deal with Thanos? The film is goin to end and I was waiting for a scene which he woupd appear but there wasn't one. Quill's father? The film used it to explain why Quill can touch the Infinity stone unharmed, but apart from explaining the plot it looked rushed, so maybe the sequel will settle on that. The climax was a good one, but the scale fell a bit short comparing to the epic first one and a half hour. Don't know what I am saying? Watch the climax of The Little Mermaid. You will see the difference.
But no error can overshadow the characterization. Really it needs a lot of creativity and script-work to make good characters for an original space adventure, but they absolutely pulled it off. Along with the silly but effective humor (opening sequence is cliche-free and matches the quirkiness of the movie), this is one cinematic experience that compels me to long for a sequelnto happen.