Firstly, that's a horrendous sample size you're basing your judgement on (unless you've watched him regularly for Basel, in which case, fair enough, that's your opinion). Secondly, to me, the issue doesn't seem to be finishing, rather his over-eagerness to impress. Whether that's down to nerves (big club, big manager, expectations etc) or dodgy decision making (inexperience at this level) is up for debate. The quality is there, as evidenced by the finish vs Arsenal (and us), for example.