Critically Taped - On outerwear with critically taped seams you only have taping at the key points where potential leakage can occur. This is acceptable, or even advantageous if you live in a dry climate, if you're more concerned with breathability than dealing with wet weather then outerwear featuring critically taped seams is the way to go.
Down - Down is the lightest and warmest option when it comes to outerwear insulation, the only drawbacks with down is it doesn't perform well in wet conditions and it's more expensive. Synthetics will dry faster than down and are easier to clean, but they can't beat down when it comes to performing in very cold and dry weather.
A fill power rating measures the number of cubic inches that one ounce of that particular down will occupy, so a jacket with a 800 fill power rating will be warmer than a jacket with a fill power rating of 500.